I need to replace the Alternator cover, and on the garage manual there is stated that one need to apply sealant on the outer part of the case, but there isnt any details on what type of sealant is required.
There are several gasket sealants that will do the job. Some are silicone based in a tube, some come in a spray can, others come in a can with a brush. I think everyone has their favorite, just like favorite types of oil. Find one for gasoline engines and I bet it will work just fine for the side cover.