It could be your bottom bracket mate, i would go and get a decent new one. Is it the axel that is wobbling, if it is i would definetly get a new bottom bracket. If its your crank that is rounded i tryed all sorts of materials, to put in but the crank eats it! (not literally!) I know a few people that have put coke can in, and i have put copper in, i have done this as copper is softer than aluminium and won't damage it further...