Experience has shown me that replacing difficult to get at items with aftermarket products is a mistake. Sometimes they are as good as genuine but more often than not they aren’t. Stem seals are a good example. They are hard to get at, involve major work and expense due to having to replace other gaskets and seals for example. So do it right and do it once is my advice. Buy genuine if available. Ask on site, a genuine head set normally includes the stem seals, a lot of them go unused as they only wanted the head and base gaskets for example, like changing the piston rings. I used to have loads lying around for the 500/550, maybe someone else has loads of 750 ones they’ll let you have foc or dirt cheap.
Viton not needed in that location so why bother.
