I can't build anything to save my life
When you do the gear diff up is oil suppose to seep out a little????
I have done everything the instruction says and can't get it right, I HATE that black o ring more than anything in the world
I've found the best way was to actually put the O-ring onto the other half on the diff housing from the one suggested in the manual
I actually put it onto the lip in the other half, then with my finger put some of the oil onto the o-ring.
When you put the two halves together I lower the thinner half very carefully down onto the larger half which contains the oiul and the o-ring