I have a 94, 850 recently purchased for my college-age daughter w/140,000 miles. In the first 200 miles of use, this car consumed nearly a quart of oil. I could see it visibly drip from what appears to be the rear-main seal. (yes, I checked that it was not coming from cam-seals up top)

Before resorting to pulling the trans to replace it, I tried STP's "Engine Stop Leak". This stuff is suppose to make seals "swell" back to normal, new condition. I changed the oil & added the product (which looks like the old sticky STP from years ago).

The car lost about a quater of a quart in the next 200 miles (much better). In the subsequent 1,000 miles it only lost about half a quart. If usage stays at this level (one quart for each 2,000 miles) I consider it "fixed".

STP advises that oil usage should stop in 1,000 miles (or it is not likely to stop at all) & advises to leave it in for the normal change interval. The real test will be after the next oil change to see if usage stays low without this stuff in the crankcase mix.

Mike