Koni Yellow Lifespan?

I've had a set of Koni Yellows on my MR2 for about a year and a half and I'm pretty sure at least one of the rears is blown already.  It's getting pretty bouncy and there is a decent coating of oil on both rear strut shafts.

Setup: 85 MR2, 250lb/in front springs, 400lb/in rear springs, good ~2" foam bumpstops, 4x "rear" inserts (front strut housings shortened for additional bump travel).

Usage: Pennsylvania backroads- twisty and frequently bumpy.  Probably less than 10k miles since installing.

Is it reasonable that these are on their way out already?  Intended for nice smooth autocross courses only?  I admit that I tend to be pretty hard on suspension components but this seems like an awfully short lifespan for struts.  I'll put the car up on the lift at some point this weekend and try to confirm that nothing else is going on under there that I could be mistaking for a damping issue.

What kind of inserts? If they're the type that get held in place with a giant gland nut from the top, my understanding is that those inserts aren't strong enough on their own and rely on the clamp force and extra stiffness of the housing. Meaning if the nuts loosen up the damper eats itself almost immediately. Check if the nuts have loosened up, and maybe apply more torque to the replacements? If they're the bolt in from the bottom type that shouldn't be a concern. Another thing is if the bump stops are very stiff or you're pounding on them a lot the seals don't always like that. But then again if they're the first type of inserts the bump stops probably aren't able to contact the seals directly.

In general my experience with konis is that they're bad out of the box or good basically forever. It's possible one or both of the dampers in question were bad out of the box in a way that would have only been visible on a dyno, and have now progressed to being noticeable on car.

They usually last a whole lot longer than that, and as they wear they gradually lose some dampening so you just keep turning them up.  Ive had them leak too, last time was out of the top.  
 

If you were the original purchaser and it is a street car then Koni is excellent about warranty replacement.  Our Mazda3 is on its third set of Konis over 180k miles thanks to warranty replacements (mostly due to rust failures).  

They are the screw-down type of insert with the big nut at the top of the strut housing, I'll be sure to double check that when I get it up in the air- in my experience struts tend to clunk really loudly when that happens, though.

Good to know about warranty, if they have eaten themselves I'll contact Koni.

I've had a Koni yellow strut on my MR2 Turbo fail within a few thousand miles, but that car was seeing track use and I suspect that that was the problem. I've had other cars with Konis and they never had an issue so YMMV.

I ran yellow Koni's on the FiST for a few years without issue, they are on a friend's FiST now and still going strong. I would contact Koni, IIRC they are pretty good with customer service. 

I ran Tokico blues on my '85 MR2 for several years on the same roads without an issue.

(front strut housings shortened for additional bump travel).

I suspect that this may be the problem.  I have  used Koni Yellows for years and they are all but indestructible. The one thing that will kill them almost instantly is bottoming out the strut. I suspect you probably have crashed the valve body in to the bottom of the strut housing trying to get more travel. 
 

Call Lee at Koni. He is a wealth of information and can probibly solve this for you in short order. 

In reply to dean1484 :

I doubt that, since the fronts are by all appearances doing great- that's why MR2 people do the shortened housing thing, so it doesn't crash all the time.

Hmmm, though maybe that does mean the rear bottoms first, nearly every time.

Bottoming even once will almost always damage if not completely kill a Koni. It is there one down side to an otherwise great product. 

To be fair hard bottoming most dampers isn't great for them...

Assuming they're the current external adjuster type, I would think that if the adjusters still move and feel like they're actually doing something then bottoming wasn't the issue.

I bought my car with Koni Yellows already installed 53,000 miles ago and they're still doing great in my Daily Driver.

Well, they've got oil on the outside and there's a lot less damping going on when moving them by hand compared to the front:

I sent Lee an email and will go from there.  Thanks for weighing in, everyone!