AM and FM issues aside (these are not interchangeable even if you are on the same band) there are to my knowledge at least 2 common encoding methods for 40MHz FM RF. Futaba have PPM and PCM which is a standard some other manufacturers use. As far as I know all of their car stuff is PPM, the PCM (Pulse Code Modulation) is reserved for the more expensive 35MHz air radios. I think the PPM method is what most other manufacturers use, I am most familiar with Hitec as that is what I used to run. I still have several Hitec receivers and a spare transmitter which I can bring down on Friday.
To be honest I would suspect the crystal before anything else though.
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