You could have an issue with the oil separator system, I see a few of these per week with either a leaking diaphram in the separator, a blocked oil return passage or both.
The oil separator is a nifty little contraption which lives under the intake manifold between the throttle body and the oil filter housing. The purpose of the device is to capture atomized oil from beneath the valve cover and return it to the oil pan in an environmetally friendly fashion. Next time I do one of these jobs I'll take pictures of the whole process and post them along with a better description.
The oil return line runs from the bottom of the separator to the dip stick tube, the tube is double walled at the bottom and the thin passages occasionally become blocked with carbon. This causes the whole system to back up and then the oil consumption begins.
The best way to check for a leaking separator diaphram is with a smoke machine, most shops have these and they save a ton of guess work and frustration when finding vacuum leaks. Since you did not mention a check engine light it's less likely that you have a leaky oil separator but it's still a possibility.
The first free and easy step would be to check for flow through the return passage:
You'll need to pull the air box in order to have reasonably easy access to the dip stick.
The return line from the OS is rubber and simply slides over a little branch tube from the main dip stick tube, slide it off with a little flathead screwdriver. Insert the straw from your spray solvent of choice into the dip stick return line opening and give her hell. If the solvent fills the tube and does not drain then you've found your problem. Proceed to remove the dip stick assembly as describe below.
Unclip the starter positive line from it's little clip thingy.
Remove the 13mm retaining bolt from the DS. Wrestle the DS tube out of the oil pan, rotate and wiggle (the dip stick not your hips... bmw's have no time for that kind of thing) until it comes out. Removal can take a minute on cars with lots of carbon buildup, just be patient.
Clear the return passage with a coat hanger or other sturdy wire, you'll have to go at it from the top and bottom, it well be messy and stinky. You may complain about the mess it's making, the poor design of the tube and the rediculous people at bmw who thought 15k miles was an acceptable oil change interval. Personally, I whistle while I work.
There is an O-ring where the stick plunges into the oil pan, the ring will usually stay in the pan recess so you'll need to remove it and re-install it on the DS tube before re-assembly. I always replace that O-ring because it's cheap insurance/headache/pissed off customer prevention.
That got out of hand, sorry.
Having said all that, what do you guys think, is it worth keeping the car for a couple of more years or should I sell it and get another car? Appreciate the input guys.
