Power steering fluid options for a leaky system

I've sealed up most of the leaks in my 89 900S, but one significant one remains: the power steering system, specifically the seal at the input shaft. I have replaced all the P/S hoses, and there's no sign of leaks at the boots on either end of the rack, or at the pump, so it's pretty much just that one spot. It's not enough that operation of the system is impaired, but it is losing enough fluid that I have to stay on top of it. Given the difficulty of pulling the rack (and having no other good reason to do so), I'd like to mitigate the leakage if possible by addressing the one variable, namely the fluid. So far I've been using Valvoline P/S Fluid, which seems to be fine as far as the system is concerned. Many others use ATF in this system, at least from what I've read. Is there an advantage in terms of propensity to leakage for using one over the other, or using something else? Do any of the additives or stop-leak products actually do anything good in this regard?

If there's no better answer, I'll live with the leak. It's messy and annoying, but with everything else I have going on at the moment, it's either an easy solution or none at all.

My old van had a leaky line; I used Lucas stop leak and that cured it.

I *think* that oil stop leaks work by causing rubber to 'swell' a bit. So gaskets and o-rings get just a tad larger and seal the hole. And they do work, when this is the kind of leak. 

If you have a torn oil shaft seal however (the kind with the inner spring around a lip), I can't see them working at all. 

The Lucas stuff is good, and has allowed me to postpone repairs for over a year on some stuff- it still will eventually take a dump, though.

I'll add - at one point I had a truck with a PS leak so bad that I had to refill the resivoir about every other drive. Left huge oil stains everywhere. After pouring a gallon of PS fluid essentially directly onto the ground, I bit the bullet and replaced the steering box seal that was torn. 

I went from avoiding driving the truck to loving it again. Just saying. 

Thanks folks. The other issue with replacing the seal is availability - being a 30-year old car from a dead brand, the seal may be NLA. It sounds like the Lucas stuff may be the best option, so I'll grab some and give it a shot. For those who've used it, how much did you put in? The system is only about 1L (maybe less), so I can't imagine using a whole bottle (unless the bottles are a lot smaller than I imagine).

In reply to 02Pilot :

I've actually drained a bit in order add a full bottle of the Lucas stuff before- it's extremely thick though, so be mindful of how much is in there when the car is cold.

My '89 has Lucas in the fluid -- sorry, I can't recall exactly how much I used, but at least 12 ounces, in two doses. It seems to be working, for now. It's been 9 or 10 months; however, in all honestly, a starter R&R morphed into the car sitting all summer, so YMMV.

Classic Saab 900 racks (and pumps??) were made by Saginaw, so while I don't know for sure, seals and internal whatnots may still be available.

Finally, R&R'ing these things sucks as much as you might expect. If you do end up having to do it, it's slightly less E36 M3ty if you take the car to a car wash with an engine bay cleaner station and clean everything down there beforehand. Also look on YT to see if anyone's done a video on how to remove the swaybar without making yourself go crazy.

Mine was low so it took a good bit............the Lucas stuff is like molasses but it goes in eventually.

Giving this an update and raising a new related question. Added about 1.5 bottles of the Lucas goo and the leaking seems substantially reduced, so that's a win. I do notice, however, that the steering feels a bit heavier than it did prior, and it also feels like there's a bit of additional effort when initially dialing in steering input; it doesn't want to change direction quite as readily as it did. I figured that this might just be alignment-related, so I checked the toe this morning - it's got a little too much toe-in, but only 2mm out of spec, which doesn't seem to me likely to be the cause.

For those who have used the Lucas stuff, and especially in 900s, did you notice any change in steering feel or behavior as a result? If so, was it affected by ambient temperature? It's going to get cold here sometime....

I did notice a slight change in the van when it's cold, as I said it's like molasses.

Only 2mm out of spec?  That's basically 1/16, so I would expect the turn in to be less responsive.

In reply to Tom1200 :

Less responsive yes, though it's likely a pretty small difference. The locknuts were stubbornly rusted in place; had they been more compliant, I would have corrected it when I measured.

What kind of a change did you notice? Increased steering effort?

When it first starts up it feels exactly like it's pumping 150 weight oil, once it warms up it's pretty normal.  Note our version of cool in the morning is 40-45 F.

My Subaru is leaking ps fluid from the pressure line. Since some of it hits the turbo, I'm concerned about fire risk. It's enough to cause it to smoke when first started.

I've already ordered the line. I'll leave it parked until it's changed.

In reply to 02Pilot :

Yes, I notice that it's a bit heavier in my '89. I don't notice additional effort when initially providing steering input. I haven't driven the car in really cold weather, so I don't know how that might affect things.

Since the stop leak has swollen the seals, would they un-swell if you removed a lot of the fluid in the reservoir  & replaced it with p/s  of your choice?  That may get your steering feel back.  

In reply to procainestart :

Good to know that your 900 did the same thing. The initial effort I'm feeling may be down to the alignment being a little off, and is just more noticeable now that the steering is heavier. Also worth noting that I've got 16" Super Aeros with 205/55s, so there's more tire to turn. Not sure really, but also not terribly motivated to do much about it right now.

In reply to M2Pilot :

I don't know if the reduction in leakage is down to the seals swelling or the viscosity of the oil being radically increased (or both). It might be something to experiment with down the line, but I've got other projects higher on the list right now. Maybe in the spring, or sooner if it becomes more problematic as the weather gets colder.