You'll have to remove the bottom door hinge and inspect it. Simple design. I imagine you will find the problem once you get a look at it.

Maybe the big steel spring is broken.

Not sure ...

on the door issue, but a look in the manual may tell you. I would look at mine and tell you but still out of town. As for the gaskets, if you use a sealer use it on the valve cover side only and sparingly. On the engine side just a dab where the cylinder head mates to the intake manifold. The right stuff is an excellent product, but be warned it does not come off easily. For valve covers I would use one of the high temp RTV silicone sealers. More important than the sealer is making sure the valve cover rails are straight and true. You will find that most are bent from over tightening. I put a piece of 3/8" steel flat stock in a vice and use a small ball peen hammer to straighten/flatten them out. When you tighten them don't over do it, use a 1/4" ratchet as it will give you a better feel for whats going on. The next day go over them again as the gasket and sealer will compress some. Mike