My diff is full of grease, as it should be, but when i want to lock it can i just put in the silly putty with out removing the grease? Is their any other fairly simple way of locking it?

Far as I know, thats the only way to lock it unless ehroof has a better idea.

Just start forcing the silly putty into the diff gears starting on oneside and work your way across. By the time you push enough silly putty to lock the diff. most of the grease will have been forced out. Clean off the diff and reassemble.

i suggest using silly putty because if you want to unlock it, just remove the silly putty and clean them up, play dough would probaly be good too.