(Copied this here from a reply on a thread in the 6.5L forum)

Since I'm in the middle of replacing my IP, I thought it was an opportune time to change the valve cover gasket on the driver side that had been leaking since I got the truck. Silly me used the Felpro gasket and the OEM torque values (whereas the chassis manual was working with RTV gasket) so now its together, but I didnt notice until I was halfway done that 20 Ft-lbs was bending the valve cover all to hell.
:help:
(Incidentally, a cork gasket is what came out of the valve cover)
I figure I'd better get this straightened out before reassembling everything else 'cuz it will be such a PIA to get the covers off again. So...

a) Is it worth trying to bend the valve cover back to normal (not sure how close I can really get it)
b) Does anyone know where I can get a new valve cover (preferrably something more rigid than the stamped OEM covers).

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I called the dealership, and since the Felpro gasket pack indicated that the same gaskets were used for both 6.2L and 6.5L engines, I had him look for some 6.5L valve covers and it turns out that from '92 to '94 both engines used the same valve cover, but they arent the same part# as the '82 6.2L (something about a change in '84?). Anyhow, the dealer told me that he could get me (a couple days) a driver-side valve cover for the '93 6.5L for $60. Though he said the passenger side was more expensive, I guess for the turbo mount on the 6.5L, but if it was the same for the N/A 6.2L I wondered how that could be. Did the '93 N/A 6.2L have asymmetrical valve covers?
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Thanks. :(

You have learned a painfull lesson about the apparent difference in the laws of physics in Detroit where those foolish engineeers write the tech manuals and the real world where where twenty foot pounds of torque is observed to be plenty enough to bend #16 steel... so...what to do?. Pull the cover, find a flat corner spot on your bench vice, or whatever you use for such violence and get the 3/8 drive extension out of your box and use it as a drift with a hammer to tap the dimple out from around the valve cover holes. Use a straight edge to see where the high spots are on the engine side of the valve cover and try to knock them back in. This works pretty well if you are patient. Way cheaper and faster tham trying to find new valve covers. I have never seen aftermarket aluminum covers for a 6.2 diesel...

I think if it were me, I would get it as close as possible to straight again. I would then put it back on with a light coat of gasket sealer on each side of the gaskets. I guess that really isn't the "orthodox" way to do it, but that's how I'd do it on my truck if I couldn't get a new cover. Of course, if you don't like that method, go to a junkyard and see if you can get a used cover there. I wouldn't mess around trying to get a 6.5 cover to work or anything like that.

i got sick of oil leaking on my engine so we took off the cover, got it straight and clean!! and then said screw the gaskets and just used black silicone, didnt have any problems with leakage after that, looks bad, works good. gonna do it again when i rebuild my motor

Most covers get bent during removal. The original sealer takes a screwdriver under the lip of the cover and gentle tapping/prying to get it loose. Just straighten the edges, especially around the holes as stated above. The silicone sealer will fill the imprefections. Get the surfaces clean and dry prior to applying the sealer. Install the cover before the sealer has a chance to "skin over". Use Brake Clean spray or alcohol to clean and dry both surfaces before applying sealer. Don't overtighten the bolts. Loctite Ultra Black or Ultra Copper seem to work best.