Just changed my fluids for my 10,000 mile. I went to Cycle Gear to buy the oil and the guy recomended Castrol V Twin synthetic 20W 50 for all three holes. I went for it changed it out and have rode about 100 miles so far with no problems. But now I am wondering if I should have gone with a different oil for the transmission. Everything seems ok though and it shifts and finds neutral fine. So I guess my question is is it ok to run 20W 50 in the transmission or shoud I replace it with a gear oil or something?

 

The regular tranny primary is 80-90w.I would not trust a 20-50w in my tranny or primmary even ifH/D says it's fine. There is a good syn tranny/primary fluid put out by Redline.

 

Do a search and you'll find a lot of us switched to Amsoil MVC 20/50 in all 3.
It's working out great, less heat, better shifting, cleaner, etc.

i.e.
https://www.hdforums.com/m_1575829/tm.htm