What additives does spectro for 6 speeds have that amsoil or any other 75w 140 gear oil doesn't have?

 

It has "superbullcrap 100" which makes it worth $20 a quart

Seriously...I have no clue. But some people will pay big bucks for anything I guess. I use the Redline Shockproof Heavy which is like $9.95 a quart. Works fine. Really ANY GL5 gear oil will work fine in a Harley trans. Valvoline 80w90 dino for $4 will do the trick.

 

I bought it and have been running it in my tranny for the last 2 years. It was supposed to quiet the 5th gear whine better than anything on the market. Honestly, I could tell no difference between it and the Shockproof Heavy it replaced as far as whine reduction, shifting, or anything else except for the fact it cost $5/qt more than SPH.
I'll be changing it this weekend & SPH is going back in.

Like KBFXDLI said- any decent gear oil will work. If $3/qt Super Tech 75W-90 from Wal-Mart will go 50k-100k miles in a tractor-trailer differential, I'm thinking it'll easily do a year or so & many thousands of miles in a little HD tranny...