The warnings about this was found after the damage was done: While attempting to fix an oil leaking right hand head gasket we found the cam sprocket bolt frozen and used a air impact wrench to remove it. That succeeded in destroying both upper and lower plastic cam chain guides. We finally did get enough force to break the bolt loose but now it's damage recovery mode. It looks like the engine has to come out and have the cases split to replace the cam chain guides due to the pins that pivot on inside the engine case. We've read about some people slotting the guides to enable replacement without the pain of the case splitting. I looks like for the lower one replacement might be possible by removing the pivot bolt on the outside of the case, but there is some concern about the one for the left cylinder coming out of position if this was tried. We saw some info about this technique, but the info. was old and we're interested to know if the method is reliable for the long haul. Is there any guidance on the size and location of the slots out there? Moe, Curly and Larry BMW repair... BTW, this 1996 R1100GS is scheduled to leave for a 12,000 mile plus trip to Central America December 30!