I have a 06 SE Fatboy and was never a great fan of HD Syn3. I have run Shockproof in a 03 Fatboy and also my current 03 RG (88"). I change the oil on my bikes and Fatboy is coming up for fresh oil. Anyone here running Shockproof in their tranny?
On a side note, my buddy worked on my clutch and when he drained my tranny, he was like "what's this pink chit coming out of the tranny?". He uses Torco in his SE 110" and that is $25 a quart but he said good for 10k miles.
I hate to tell your buddy, but
any gear lube that meets current API specs is good for a lot more than just 10k miles. There never has been a legitimate reason to change the trans lube on a Harley every 5k miles, and now even Harley has seen the light and changed the maintenance schedule to 20k miles.
Think about it this way, how often do you change the gear lube in the rear axle of your pickup truck or rear wheel drive automobile? Never, you say. Well guess what, those are much tougher conditions than a Harley trans will ever see, short of the drag strip.
Use whatever makes the gearbox function the smoothest, and I still recommend the red stuff so you can easily tell when the cheap assed seals start leaking. I use Shockproof, but I have also used Bel-Ray Gear Saver in the past with good results.
Jerry