Right they prolly didnt even do a check on his intake manifold and just assumed.
The only reason id be scared to use MMO is to much sludge build up will eventually clog something if you break it lose.
Im changing my head gaskets right now and when i pulled the head i was happy to see no sludge build up at all, makes me happy.

 

What plugs did you put back in it? Plain jane champion coppers are the best. If thats not whats in it I would start with that.

 

This is a good point other plugs are know to cause problems.