I'm using M1 HM in my leaking Firebird right now. I have some Pennzoil HM in my stash for an upcoming change after I use up my next bottle of M1 HM that I have. Good to see that it seems to hold up well, aside from the shearing. I plan on using their 10W-30, which should be a bit less prone to shear. The shearing didn't seem to affect anything at all, wear wise, so I wouldn't worry about it.