I remember old days all my Ute's needed fish oil, to stop them rusting. used to smell bad!!
It sure does smell bad. Used it a lot when I was a working on old cars to fix/stop the rust in the old cars. If they know its a problem why not treat them in the factory when they put them together, not hard! If the bike was a few years old I would say that's life but fuck me I only picked it up 2 months ago. My sporty is 4 years old done 72'000K's and not a spot of rust on it.
Every Harley frame and swing arm ever made has done this .
My 2011 fxst , has Never done this. Ridden in rain all time. Even rode Perth to Melbourne in torential rain 90% of the way. And cant find any rust anywhere.
Your frame is sealed or the holes were above any fluid relief hole height.
Except Twin Cams, no rust in or on Twin Cams ever.
Don't waste your fish oiljust wait for the transmission oil to find a way in there