I had the same problem with the gear diff. When I put them together you could see light between the 2 halves. I sanded the side that fits inside the other and kept dry fitting with the oring and the gasket. Once i got it to the correct depth, no more light between the halves, I built it, inserted the screws. Initially the screws were too tight and bound the diff up. Backed the screws off 1/4 to relieve the pressure and it works like butter with no leakage. I also purchased a spec r Gear diff separately for the front and did not have the same problem. It went together perfectly. I think the mold for the parts in the R1 are off in size and make the 1 diff half too large.