After a bit more searching found references to Hylomar or MB 003-989-98-20-10

Looks like I may have been able to avoid redoing the process if I had applied a thin coat of hylomar to both surfaces of the gasket (I have hylomar and have used it to seal machine tool surfaces which see lots of oil, says its good agains automotive fluids including oil), the MB stuff looks like it would work fine as well.

Oh well still need to putll it apart again, may as well get a new gasket while I do that and probably use a very thin coat of sealant.

Still welcome comments.
Paul