I have a 93 945T with about 240,000 miles on it. I've flushed the transmission fluid at ~50,000 mile intervals using conventional ATF since I bought the car in 1995 with 40k miles on it.

This past summer, the transmission started becoming "reluctant" to go into reverse when it's hot. The transmission seems to remain in neutral for a while until reverse eventually engages. This takes anywhere from just a second or two up to say 30 or 40 seconds. Moving the selector back and forth doesn't seem to do anything to speed up the process, you just have to wait and it eventually drops into reverse. It is definitely temperature related as it almost never does this now that the weather has cooled down.

Otherwise the transmission shifts fine regardless of temperature.

I could live with this minor inconvenience but I'm worried my wife or son will be in the middle of city traffic or in the middle of nowhere and the transmission just quit completely.

Is there any chance changing to Mobil 1 or adding an additive to the fluid would help? Everyone recommends against changing the filter screen, is that even worth checking?

Any information or suggestions would be appreciated.