Yesterday, I changed from the gear diffs over to the ball diffs.
Though I'm not a fan of ball diffs, I've to admit that I'm really impressed.
I used the recommended 3 spacers crown gear side and multi purpose lube.
The gears felt very stiff in the beginning, but they broke in immediately creating a very smooth and nice feel of the drivetrain.
Performance of the ball diffs is still remarkably better than the oil-filled gear diffs, but they're a little on the tight side right now because they're just breaking in.
Though the teeth are much smaller than the teeth of the gear diffs, I'm sure they will hold up to the Basic 4200 since the gearbox allows for absolutely no flex
BTW: not locking the diff rings to the outdrives by pins, D-shape etc. seems a good idea - my diff rings will slide on the outdrives before the balls begin to slide on the diff rings under severe force and saving my diffs.
The only drawback is that a complete ball diff costs around 50US$$ here in Austria, where I could get away with 17US$ for the RT-4GP gear diff
And that's what you get on 8 cells BL ...
I've run through about 40-50packs and the SB-Sport didn't need any maintainance yet and there isn't even anything that seems to go soon - we'll see how the ball diffs do their job