I think since the 70's, these seals were fairly standard on all Japanese motorcycles (I think even the OHV Honda CX models had them). OHC almost always run the cam in plain bushings and need lots of oil pressure up there for it (so a lot of oil).That’s an interesting point about the difference between OHV and OHC engines that I hadn’t appreciated before; I thought that they
(OHV) only need valve stem seals on the inlet valves because during the inlet stroke the depression in the combustion chamber would draw oil down the stems of the inlet valves but the exhaust valve guides wouldn’t leak because the ex. Valves were closed, and when they were open the gas flow would be pushing oil back up the stems.
There you go!