[Alex V.]

If you do the MMO and it still comes back intermittently I'd put some thinner oil (Rotella T5 10w30, Valvoline Maxlife 10w30/40, etc.) in it and put the prescribed dose of Seafoam in 500-1000 miles before the next change. That's plenty of oil pressure so I personally wouldn't run a 15w40 unless I was towing heavy, a lot.

I ran Schaeffer's syn blend 15w40 in my '85 C3500 (got it at 77K, 128K now) and while I don't believe it did any damage to the engine, when I changed to 10w30 of the same line about 10,000 miles ago the truck's manners improved substantially and oil pressure stayed within 5-7 PSI of what it was. My dad was of the old school that, quote, "If you put 10w30 in a big block you'll be looking through it in short order" but as I slowly gained more knowledge of oil chemistry improvements since the time of our trucks I have no fear in using a thinner grade because modern lubes don't shear (get thinner with use) nearly as much as they used to.

Also, I use Maxlife in 90% of the vehicles that come through my shop, from Honda's to Chevy 6.0's and Vortec 350's; it has shown some very good results, including keeping engines in one piece through repeated 15-20,000-mile oil change intervals. I also can usually notice some internal cleanup over a couple correctly spaced changes. I believe Schaeffer's cleans better than Maxlife but that coupled with it not being a high mileage formula seems to have the possibility to open up leaks if it's already leaking some or right on the brink. My 454 leaks quite a bit of it but that's just more motivation to re-seal the whole thing and adjust the valves in one fell swoop.