I think switching to a manual could be done, but hard to find a manual trans....
Low fluid could cause this problem....
I recently had a hard time trying to measure the fluid in my 1989 300E...
What people on this forum told me to do is (I added a bit more info in too)....
Park car on LEVEL surface, wait until next day (CAR IS COMPLETELY COLD!!!!)
In morning, start the car, shift through all gears like so...
P to R, wait 5 seconds (TIME IT!)
R to N, wait 5 seconds
N to D wait 5 seconds
D to 3 wait 2 seconds
3 to 2 wait 2 seconds
2 to 3 wait 2 seconds
3 to D wait 2 seconds
D to N wait 5 seconds
N to R wait 5 seconds
R to P wait 5 seconds
then apply parking brake and get your butt outta the car!
keep engine running!
get to trans dipstick
remove and wipe clean with lint free cloth (DON'T EVEN THINK ABOUT USING A PAPER TOWEL!)
reinsert dipstick COMPLETELY!
REMOVE WITHIN 2 SECONDS!
measure...
fluid should be 10mm (1cm) below the MINIMUM MARK (LOWEST INDENTION)!
DRIVE CAR ON HIGHWAY FOR 15MINUTES!
recheck fluid on level ground and with engine running!
try not to spill AT fluid on exhaust manifold... makes white smoke and brings you THAT much closer to getting cancer...
Fluid should be at MAX INDENTION! (Highest indention!)