I just had my wife's 1989 290e 2.6 transmission apart, for the same problem: reverse failed.

I found exactly what Mr. Brotherton described, only not as far gone. There was no evidence at all in the pan. The fluid looked prety good, but not really clear.

The reverse clutches no longer had the little springs to hold them apart, so they were worn out, although the steels were fine. The big ring on the clutches was cracked. The rest of the transmission was like new (except the seals, which were like hard plastic). You could still read the printing on the inner surface of the bands.

My rebuild kit had clutch plates, but only 4 of each type, so I had to buy two more from Mercedes. (I figured I would replace them all, since I had most of the clutches anyway.) Total cost: $135 for the kit, $95 for the parts from Mercedes.

As Mr. B. said, you don't know until you open it up.

Andrew
1989 190e 2.6
1990 Jaguar xj6