Maybe base gasket for the power head I believe mine is leaking. Hard to tell with all the oil over the shaft and everything. So I cleaned it get a better look. I tighten up some of power head bolts to be sure. We’re a little loose. But take the cover off to get a better look
agree. NAPA would be Sierra gaskets -- but the whole assortment, and that is a cost and convenience advantage. I've had good luck with Sierra products generally, but oem would be preferable. Maybe a shop has a packet -- dusty old NOS package on a back shelf.