Built multiple Xray gear diffs. Haven't had any major leakage issues. At worst, it weeps just a tiny bit, but not enough that it required me to refill the diff often.
The Schumacher gear diff, have built two of them and 0 leakage so far. I feel the design is more leak-proof than the Xray and it is less than half the cost. The main downside is the largest spur is 88T.
The Arrowmax diff, in my opinion, is junk. I have fitted an Awesomatix gear diff to an F1 car as well and it is good too, but a little more work than the Xray/Schumacher diff.
Thanks for the insight. The Schumacher diff does seem like a better option given the price is half of the xray and arrowmax. Doing a bit more research on the arrowmax diff and seems like everyone thinks they are junk, be it fitment issues or just right out design flaws. I do see they have an updated version of their gear diff recently. No report/reviews yet tho. I didnt even know awesomatix have an gear diff option for an F1, I should check it out too.