Makes me wonder how many other pulleys are going the same way.
If the magnets only good for standard torque and we crank it to +150% of that - it may be slipping more than we think.
1) how to measure slip?
2) how to improve if needed?

I'm not sure what stopping it by hand at idle means ...? Is that with an engaged magnet or not?
I recall from Woody's LED test that the magnet stays engaged once over 2000rpm in Drive and until the car is turned off (but don't quote me)