Ironic you post this as I have been doing some research on this very issue based on the unusual code we have also had as I would like to be a bit proactive myself in replacing some parts but have not read of a PM position when these parts should be changed. The concensus seems to be by 80k but guess that would be based on extreme conditions.

So I have 2 questions for you...you mention the mechanic changed "gaskets"...did he actually change the cover with the diaphragm in it or just the gasket seal around the cover to the manifold? I have heard this diaphragm can rupture causing what you experienced. Second, I have also read that if issue is bad enough the dipstick tube needs to be removed and seals cleaned and as JCL mentions the ancillary lines as well but I could not find that thread relative to the dipstick tube to cite in this response.