My '93 190E 2.6 lost reverse quite suddenly. I was driving it to diagnose a rear-end shake. When I tried to back up I had no reverse at all (reverse worked fine before the test drive, and all forward gears still work).

Now, when first started, it will attempt to move in reverse (will go about a foot on level ground) but that quickly fades to no reverse at all.

The fluid level on the dipstick was fine before this happened, but now shows the level as being too high (about 3 inches too high on the dipstick).

Could it be a stuck valve in the transmission?

Thanks.
Brett