I use Red Line lubricants in my Dyna. Is Red Line transmission oil better than Belray or Spectro? I don't know. Short of some very sophisticated testing, I don't think that any of us could know. Red Line is not as readily available as most other lubricants at local parts stores. I just have to order it a few days before I will need it.
While Mobile-1 is a highly rated oil, I have heard a lot of riders complain that their engine, transmission and primary makes noticeably more noise when they use this oil. Does that mean that Mobile-1 does not lubricate as well as other oils? No. Without someone testing this oil for wear properties, it just means that it is 'noisier' than some other oils.
Red Line transmission oil is fully synthetic, Belray is not synthetic. The primary advantage of synthetic engine oils is that they tolerate higher temperatures than conventional oils without breaking down. In a primary or a transmission, high temperatures are not an issue. I can't see any reason why Belray would not be a viable lubricant in a Harley primary or transmission.
If I ever need to change primary or transmission fluids and didn't have Red Line handy, I would have not qualms about using other high quality lubricants.
Pete
I ran Redline for years. Figured I was sick of ordering it. Mobil-1 is at stores.
Redline stayed in trans last 2 changes. Mobil-1 came out pink. I've also been wearing a 3/4 helmet.
This weekends 200 mile ride, I wore a half helmet. Drove me crazy...... I started hearing it the other weekend in Virginia.......with the 3/4 helmet.
All the Redline is flushed out now.
Bel-Ray Gear saver is 85w140. Wingnut swears by it. Thick and red. Like a candy apple. Non-synthetic. Hypoid rated.