Interesting theory, but the funny thing is that what looked like a sleeve on my car isn't just limited to mine. It's also on my old engine, and it looks like it's on the photo I posted that I pulled off of Diesel Giant's website.

Anyway I pulled the bolts from the old engine so it'll be proper from now on but haven't been able to get any hardware to see if I can put a nut on the portion of the bolt that protrudes through to the under side of the housing. This should fix it and keep the stud held firm so the lid will stay on tight. Still convinced there's a "sleeve" of some kind and curious how it's held in there other than magick.

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1981 300SD - 283,000 KM's at purchase, 360k+ now. Engine replaced at 311k. 16" CLK wheels, w126 gen II cosmetic upgrades, late w126 leather interior. RIP. Parted and gone due to fire

1987 300SDL - 243K miles and counting. In winter hibernation!

2001 Ford F250 Super Duty "Platinum Edition" Lariat 4x4 7.3L turbo diesel, 295k+ miles, various mods for reliability and performance.