I once brok a slug because I was being an idiot and using a metal hex key (BIG nono
) instead of a plastic diddle stick. Slugs can be replaced with ones of similar dimensions from other parts coils/sets as long as the threads of the inductor are not shot. It might be a good idea to look into a plastic safe lubricant for them...
EDIT:One thing that might loosen your slug is (provided the wire is thick enough to stand the current) with the set turned off connect a D cell battery across the coil and let it warm up until the slug loosens up, then remove the battery and the slug and then quickly try to clean any wax or other gunk from the slug and coil threads before it cools....IIRC I did that to free the frozen lin. slug on my CTC4.