Oil pooling in '68 340 factory intake manifold....

Ok my 360 is doing the same thing,thing is if we pull the bolts clean,add sealant what about the threads in the heads if there is still oil on them that silicone is not going to stick,now what.

I just cleaned mine with WD40 and paper towels... then used black permatex on the threads... no leaks for 2-years now