Stop worrying about the misting. I fitted a VH style oil tank to my RH500 earlier this year (it having previously had a 350 size oil tank, petrol tank, engine and gearbox. The oil tank was the last thing to be changed, engine and gearbox being up to the 10,000 mile mark when the oil tank was fitted). I had sprayed the tank with an aerosol and was somewhat annoyed when the black paint turned greyish behind the carb inlet. So it is obviously spitting fuel back at the oil tank. My engine is on a standard A6/664 cam and tuned correctly. Both Rob Jameson and Andrew Grant (amongst others) will confirm that HUG 746 performs well as an RH500 so I can only conclude that the spitting back is a standard fitting.
Ride the thing and stop worrying.
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.