I was not aware of that video! Thanks to Eric and also to Mick for pointing it out.
Because the starter is new, if you pull the starter and confirm oil got inside it would make sense that the warranty may be honored. Since you replaced the vent and also did not overfill the primary it's reasonable to conclude that the inside oil seal or the starter clutch seal was defective.
Worst case, if they don't honor the warranty, you could install a new inside o-ring and drive clutch ($100) yourself rather than going for the new style starter $500 . It really depends on how deep your pockets are. In my opinion, overall the original starters are excellent unless of course the primary gets overfilled and/or the vent is clogged.