The elec plate with the solenoids might be the issue as many have had that problem here on the forum.
The other quick check would be to look under the cart before moving it to see if fluid is on the ground and if so it might be low on fluid. Still if it is low there would be a reason for that and a fix needed.

The O ring for the electrical input plug does sometimes fail on these trans so that could be the issue as well. The O ring is a pretty easy fix for a DIY if you are mechanically inclined but the plate is much more involved.
The plate can be had for around $300 and install depends on who you have do the work.....you doing it would be free of course. The O ring is around 7 bucks and fairly easy to do.
Good luck either way these cars are a lot of fun and pretty reliable if you take care of them. As with any automobile if abused they will let you know it with frequent problems.