I have used the Mobil-1 75W-90 & am currently using the Spectro 6-speed. I notice NO difference in shifting or 5th gear whine in my '07 Deuce. Both are superior to Formula + for tranny IMO but I use it in my primary.

 

thanks for all the replies. i am using the mobil 1 right now but have been doing some reading on the Spectro for 6 speeds. didnt know if i would see a difference between the 2.

 

+1 on redline thats what I use and it has improved my 07 noise from 5th. My bud has spectro in his and he is happy with it.

 

I use the Spectro....no complaints... well other than the price... just paid $22 for a qt at the dealer :-( ....but it's great for the tranny.. and I plan on keeping it in for 20k miles..... I just drained the tranny to replace a leaky clutch cable and the spectro I put in 10k ago, looked good as new... I did however, put in a new quart...just because I don't believe in reusing any kind of oil once it's been drained....

 

I know this is blasphemy, but I use to run it in my Ninja and it made my tranny shift like butta! I've wondered if it would do the same in my Harley, especially since the tranny oil is seperate from the engine. I'm assuming it would hold up better too.
Also I think this Spectro is a synthetic blend, not a full synthetic.
Lots of $$$$ too!!!!