A great sealant use in that application is a copper head gasket spray. That stuff is tacky and works great!!!

 

I have found that the key to using straight RTV is using it properly. As already mentioned, both surfaces have to be absolutely clean and dry.
I used straight RTV on the rear end cover of my 95, and others, and never had a problem with leaks. I cleaned both surfaces with carb cleaner down the bare dry metal, put a thin bead on both surfaces, left it just tack up, and then put the cover on just finger tight. I left it set over night with no oil in the axle, then went back and tightened the cover bolts the next morning and filled it with oil.

 

Another option instead of using adhesive.

Cut the heads off a few spare bolts to use as alignement dowels, slot the bolts with a hacksaw and use a screwdriver to install and remove. Slide the manifold on, bolt down, remove alignement pins.