This might help.
http://www.astronomysite.com/mapug/22/msg22662.htm describes RA lock and a couple of set screws. This may be your problem.
Other than that
http://www.sfaaa.com/content/view/20/71/ shows some major surgery. if not try googling for "Lx200 disassembly", "LX200 RA lock repair" or something similar.