^Gotta love those old training films!
An open diff applies equal torque to the left and right wheels, regardless of speed. If a wheel is slipping, the torque it takes to make that wheel slip is all the torque the other wheel on that axle will get, and giving it more gas just spins the slipping wheel faster. The power that two wheels on an open diff axle can put down is limited by the wheel with the least traction.
TL;DR: if one front wheel is spinning and the other isn't, that's normal for an open diff.
Also, don't worry about auto hubs, those were a WD21 thing. Your R50 came with drive flanges, which have no moving parts and should be pretty much bomb-proof.