I've had 30 spline Mosers in my 8.75 for over 20 years. I had those same axles cut down and resplined when I did the Scamp. Never a problem. And BTW CB is correct, no one makes a 40 spline for the 8.75. I think you just got a crappy axle.
Guitar,I had mentioned picking up a Dana complete and maybe getting the 40 splined axels and spool for it.Best to build for future power adders.:toothy8: