2mm on the gasket is fine. Use a Renix gasket to be sure. For fun, match the intake to the gasket and the head ports to the gasket like I did. But, I , like Mike, am not convinced this is a vacuum leak. Heck, I'm not convinced it's a leaning out problem!! As for cams, I think we're splitting hairs here. If the engine ran that lean, there would be driveability issues. I'm thinking it was probably not bored correctly to the piston size.
I am also doubting the lean theory, unless he has an entirely new heavy duty over sized cooling system keeping the engine from overheating the coolant and boiling over. And any exhaust problems, like a clogged cat would cause noticeable problems as well.
I had a Dodge Charger lean burn, '76, 400-4Barrel, that cooked the cooling system, wiped out the Transmission 7 times (cooked the T fluid), blew hoses and 20 lb caps like clock work, but the engine kept running, and it never used oil in the 4 years, 78,000 miles I put on it.
A bad bypass valve on the oil pump would show up on the dash, but what about air entrainment, it would show low pressure too I think?
Leaking injectors at shut down washing oil off the pistons?
I like your machine shop screwed up idea, but they have screwed it up more than once now if that is the case, right? What about a warped block?
One bad leaky fuel injector might make sense. It wipes oil off the piston causing damage, causes 1-2 other (next to fire) cylinders to run too lean as the O2 sensor compensates a little late, but does not run the entire engine lean, just one rich (leaking injector) and one lean, the next injector, and a little excess gas in the oil causes piston scoring?
Does not take long for one leaky injector to trash an engine, with little warning on a non OBD-II system from what I have read.
