This sounds very familiar. Our 1989 190e 2.6 had about 220,000 miles on it when the transmission started slipping in reverse. The fluid was not really grey. It was still pinkish, but definitely had some pigment in it that took away the bright clear red.

It turned out to be the powdered remains of a spring holder. When it lets go, the reverse clutches are always slightly engaged, and so, obviously, wear out quickly and cause the problem of loss of reverse gear.

I did the rebuild myself. There are several recent threads with the necessary information. Manuals are available for the downloading. If your problem is the same as ours, you will need a gasket and seal kit, the reverse clutches, and the broken bits that you find inside. The rest of our transmission was still like new. I could still read the letters printed on the wear surface of the bands.

So, not the kiss of death. Only the kiss of surgery.

Andrew
1989 190e 2.6