I now have a full size servo controlling the shifter.  It's so much stronger than the micro servo I tried and doesn't heat up at all.  I think that issue may now be resolved.
I also put this stuff in one rear axle to try out.  It looks like it'll work better than the 2.5M weight oil I was using and shouldn't leak out.  Now to do the other rear axle.  No need to do the front axle, though.  I have something different planned for it! 
I'm also starting to make some progress with the ESP32 MFCU.  I have the steering worked out, but that's all.  I still have quite a bit of configuring left to do.  Having to also learn a new transmitter just adds to the complexity!