I've been using the M1 75w90 for a couple years now. No issues and the oil is much cleaner when I change it than it was when I used the merc crap, and costs less. I have also noticed the merc stuff changes to sludge if it sits long enough.

imco recomends torco in there drives any reason why?

+2 on Amsoil

amsoil definatly, but if smitty says something different on high horsepower do what he says, he is highly experienced on pushing stuff past its limits.

I had real good results with Amsoil Severe gear over everything else I previously tried. I am now trying The Bravo shop Neo but I haven't had conclusive results yet but I will report as soon as I know something, Smitty

Has anyone running a high HP motor on a Bravo or Alpha drive on a 10 or more year old drive had any failures (shafts or gears) running synthetic or conventional lubes? I know this is not scientific but may show pattern.

Knock on wood.. stock 22 yr old alpha, Merc lube. About six years running w/three different motors 420 hp to 560hp sbc's. Found a late 80's alpha ss drive switched it out w/428 sbc around 640 hp, 6500 rpm..been running amsoil in this drive.. knock on wood again lol no drive issue's

I have been running Amsoil with Lucas the last couple years in my 17 year old Bravos with no problems. Oil looks really good and no metal on the magnets when I change.

If you treat them right, the alpha one is a dependable drive and not as delicate as some think. With syn lube, drive shower, lube coupler, gimble they can last with higher than just 350 to 400 HP Small Blocks.

I believe they are more prone to failure with high torque BB. IMO

I build a fair amount of Bravo drives that go behind some decent sized engines (some well over 1000 ft lbs of torque). By no means am I an expert on drives. However, I have had some very good luck with them staying together. I have been using the Merc HP lube with a gear lube additive from Pro Blend. I've noticed 30-40 deg. drops in oil temp and a huge reduction in pitting of the gears. That's what I have seen as the biggest cause of failures with built drives. The stock XR's seem to break one of the shafts before the gears go.
I've tried Mobil 1 gear lube with the Pro Blend and had a problem with clutches hanging up and sticking. After a hard run they wouldn't come out of gear. If they did, then they wouldn't go back in gear. Most of them would need the forward gears replaced with the clutch since the clutch would tear them up.
I'm sure there are other good choices for lube but this has worked for me.
Eddie