I had trouble getting the LH valve cover gasket to not weep or leak at the semicircles at the front both times I have had it off for valve checks. Both LH semicircles leaked again this last time and I pulled that cover off Sunday to fix it. I discovered I mucked up the little sealing ridges that mate against the cylinder head when I removed the RTV sealant I resorted to last time so I ordered a new gasket. Ouch! The service manual says not to use any sealant except at the semicircles but doesn't say what type. The RH side sealed fine with Hylomar which is easily removed later but I resorted to high temp RTV silicone on the left one after Hylomar leaked. I damaged the gasket digging at the silicone to remove it. I learned later that letting the gasket sit in a container of gasoline softened the silicone enough to easily remove it but I damaged the gasket before then.
Anyway - the Q is what does Honda use to glue the new gasket into the valve cover? It appeared to be a clear sealant with light adhesive properties applied to the upper surface to glue and seal it into the valve cover but it let go easily when the gasket was pulled out of the cover. The gasket's lower surface is designed to seal against the head without any sealant except at the semicircles. Honda techs told me not to use any sealant at all as the semicircles normally seal up without any problems but the upper surface is definitely glued in place. They never remove them from valve covers so had no clue what to use.