XRAY - Model racing cars

I have rebuilt my diff after changing oil. I left the diff to stand for a while to see if there is any leaks and nothin dry as a bone. Put the diff in the car and there seem to be a some oil on the shell and and on the suspension tower directly above the diff I have built to the manual so should be good also used new o-ring and gasket

Also I have not overfilled it

Take it apart, remove the O-ring then put it back together, should be fine then.
The O-ring gets trapped and causes problems

Yep, the only diff I ever had leak was due to the o-ring getting mashed up in the wrong place.

As Damian says the o-ring seems to be unnecessary, not had any leaks without it.

Use only the gasket!!