A little out of order - run it til it will not crank over anymore. Then either siphon any remaining fuel out of the tank with your fuel bottle or turn it over holding a rag over the open fuel tank. Then do the ARO routine....

With it off the ground, turn wheel by hand and the other wheel on that diff should turn the opposite way. Repeat for the other end. With it in the air again, hold one wheel against you so it can't turn and turn the other wheel on that axle. The wheels on the other end should rotate in same direction as the one you're turning. This was how Misbehavin said to check the diffs for probs.

Spur gears on these have always wobbled. I assume this still has reverse??