Ok so I have a 1998 e39 520i and it came with a welded diff. And it is not that great so i want a normal diff but don't know much about them. So don't know which one to get. Also I bought it thinking it would be great to mess about in private tarmac or what not but it will not go side ways(Maybe it's my driving) so just want to go back to stock or even a better one than stock if there is such available.