A friend has a minor leak around his 1991 Civic valve cover.
He replaced it with a new Honda OEM about a year ago and it
recently started leaking again. I vaguely remember mention
of an aproved sealer that could be sued that would mess up
the O2 sensor. I tried going back and searching with no luck.

He has a new OEM valve cover gasket and would like help changing
it Monday evening. Any suggestions as to what type sealer is
good?

Terry