Differentials = Balls (are gear diff gone forever?)

[chb]

Re-staring RC, and gearing up, I met only cars with ball differentials...

What I don't like about them, is the requirement for maintenance

My first question(race) is : The advantage over gear differentials is only the ability to reduce freedom (by tightening). We could envisage the same with gears after all : very high viscosity grease(coarse adjustement) and slight tightening(fine adjustemen). Do you agree with that ?

Second question(play): for bashing around with insane motor power, ball differentials become the real weakness. Can some cars be fitted with gear differentials(I mean not toys, real cars like B44/B4, BJ4, zx5/RB5, D4, ...) ?

Thanks!