Right, first test drive completed. 12 packs of 8 minutes each, so about 1,5 hours worth of driving. And it went a bit like I expected...somewhat.
Good: Durability - These things will last a good while, but not forever (read further down to see why), awesome forward traction, consistency (wont burn out or readjust ifself like ball diffs). Apparently easy on driveshafts aswell, but I did swap the lot for new ones before the test and they showed no wear.
Drive feel was almost excatly like ball diffs, except for the forward drive. The included oils were spot on for the track (high grip carpet). 5000 front, 2000 rear.
Bad: Hard on belts if slipper isnt adjusted just right. First lap, first bit of hard braking and the horrible noise of belt skipping presented itself. Had to tighten the belt one notch. The belt is fairly new and the pulley is obviously all new, so it wasnt a wear problem. Nothing under acceleration.
Did they leak? Well.......yes. They did leak. I noticed about what seemed like half a drop(ish) of fluid on the rear diff outdrives and about the same on the front. The front I left unchanged (for comparison reasons), but the rear I decided to take apart to check its internals and see if I could fix the problem. The internals are just like any other geardiff, so nothing new in that compartment. One thing worth noting here - the spider gears does come in contact with the case, causing some rotating marks. Whether that'll mean anything in the future, I dont know. Time will tell.
I also noted a large amount of play from the outdrives when tugging it when the diff is assembled. This struck me as odd and could be contributing to the leaking.
Took it apart and put a 5x7x0.5mm Schumacher spacer in between the bearing and the o-ring to compress the o-ring a little further and also to bring the crown gear closer the spider gears. This didnt cure the problem, but it sure helped. The diff felt notchy as I reassembled it, but the slop was well and truely gone. Was a little worried about going overboard with the fairly thick spacer, but 11 packs later and the action is now smooth, so it was just a matter of breaking it in. The leaking hasnt been completely stopped but only a very small amount was found under the bearings. Something like a quarter of a drop. I can live with that. The bottom of the car is bone dry. So is the front of the car, despite the heavier amount of leaking. I estimate about 2 drops excaped from the front diff which was left completely unattended throughout the day.
The front diff will need the same solution as the rear, but I ran out of spacers (needed 4, found 3...obviously) so that'll have to wait.
So, are they worth the price? Considering the leaking and play in the outdrives, no. Slash 20-30€ off it, then yes, absolutely.
I'll be using them instead of the ball diffs, but I'll keep the ball diffs for loose surfaces since I have my doubts about geardiffs and slippy surfaces.
No oil on the chassis.