If the 18's are happening 1st. check those auxillary contacts of M. By check I mean replace, and see where you go from there. As I said I hate intermittant 18's. Any contact between STP and P or any circuit that would cause the contact to drop. Data loggers come in handy on this one.

It Don't mean a thing if it aint got that swing.

Cool, Free, Johnny Smith courtesy of NPR..HERE
http://www.npr.org/ramfiles/asc/asc25.smith.asx