300SEL delayed reverse

[acerejo]

When I shift into reverse there is a couple second delay before it accually engages. I am also noticing that there is a slight slip between shifts when car is cold. I've changed the fluid and filter even though they were clean. The car has 185,000 miles and is otherwise OK.
Question: can these problems be corrected without going through the whole tranny? Should I keep on driving and eventually go for the rebuild? Is there any additive that really works?
Any input woulkd be appreciated, thanks in advance,
Armind