These guys all know their stuff.....

best advice I can add for a new em trainee technician/owner....

*waves two fingers in arc pattern*
"this is not the faulty relay you are looking for"

Might be just my bad luck for the last 15 yrs but....
Its never the easy fix, easy access "quick adjustment with a leaf tool" relay contact..... its the last one on the chain of switches on your faulty circuit.... the one that doesn't even look like its part of the faulty circuit in the schematics..... the one that's the biggest pain to get to... behind the most ceased screws to slip your flathead off of and gouge a finger....the one that has no contact surface left and needs replacing.....
and that's after you've fixed all the other 120 leaf switches and mastered reading complex schematics.....

properly caring for an em is going to be work.
Seen too many good projects abandoned or worse, destroyed because the owner wasn't ready for or aware of whats in store.
but its HIGHLY rewarding to play a smooth one, especially when you made it so.

just be ready for some grubby knuckles and popped brain cells is all.

I would say it was most likely demagnetized by the oscillating emf fields generated by the buffers induction motor itself... tricky problem that magnetized/sticking relay. Iv'e had plenty of score motors perpetually spin due to a stuffed or bent zero switch but not a relay... unusual one, well done finding that!