Monkey diff spring
 

I am just in the process of buildingh a MM kit, come to assemble the diff but the spring is noticeably to large to go into the drive cups. Its not just tight its to large a diameter by some way too.

I cant see an alternative spring in the kit so i am assuming this is the right one, any seen or heard of this before hand ?? Any ideas on how to get this in and compressed ok ??

Are you sure it's not the slipper spring? Which is bright chrome.
The diff is dull metal and smaller

+1 diff spring is black/grey in colour

I had this problem too. I sanded down the outer edge of the spring to fit it in the drive cup.
If you have a dremel tool:
put the sping on a small shaft like a screwdriver then sand it down with the dremel. The diff spring spins on the screwdriver shaft and it gets sanded down nice and even.

I ended up just dremelling it down slightly, it didn't need much off it in the end but 100% wouldn't fit without this doing.

Was fine with mine, although I did get confused with the springs for a bit as there are a few, and some are black so they hide away in the set of parts ;)