Gearbox oil

I suggest you ask on the Facebook page (https://www.facebook.com/groups/10302209470), which has lots of U.S. members.

You should be able to get a full synthetic oil for the gearbox stateside. Many use this instead of the EP90. I think it is 75W-90, GL4 suitable. It makes the gear changes quite slick, and will be a big bonus if you use the bike during the winter.

I have some synthetic oil in my gearbox as it was available locally. COMMA brand, seems to work well. 

Jon:

Try asking around at any number of shops that specialize in the repair of old MGs and Triumphs.

They should either have it or know where to get it.

Mike

Harley Davidson uses SAE 50 in the early models and a newer type (ie EP90) same thing almost,  in the big twins. Top noych oil and of the highest grade possible. 

EP90 used to be common in farm shops here until recently, not any longer.

I'm sure HD charge a lot extra for their oil, it is just badged, so I would assume readily available under another name in the US.