I'll chime in and mention that before I changed out my trans filter, I had no hydraulics and no reverse. It would randomly move forward a few feet at a time, but you couldn't make it go on command. Put a new filter on and it was like a new trans was dropped in.
Even though the fluid on the stick may look ok, I would suggest doing a complete filter and fluid change. The steering and reverse gear behavior sounds like you may have some contaminants in the system.
BTW, that's a heckuva machine to mow an R/C airstrip. I hope your flying buds appreciate it.
I would have just gotten them a Yard Machine off Craigslist, lol.
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