Hi Pracy
To try and answer your questions
It doesnt look like the gaskets leaking but as you say the other end, when you build them do you grease when assembling that end, you should grease inside the metal part of the diff case plus the outdrive shaft that goes in as well also grease under the large washer (not lots) and around the o-rings especially, if you look through theres lots of info for building diffs that wont leak in this thread.
dont worry to much re shims i never used to shim mine at all and never had a breakage, i now use 2 shims to open the gap making the diffs much freer it makes a big difference placing 1-2 shims the other side of the crown gear boy does it spin now, the UK mugen driver i spoke to recently said you can run the diffs very loose on the mugen as you will be hard pressed to break the gears
I do the same as you push the pinion gear in then push cvd on and then tighten down so your good there, perhaps allow a small gap for a little play between bearings and cvd.
I think you only get the 2 wahers for the wing in the kit but its been a while and i could be wrong.
HTH
