Do stepper motors get old?

I did a mill conversion in 1998. It has 42 frame steppers. I've been
reworking it, and I've been told modern stepper motors work much
better than earlier designs. I asked a motor vendor, and was told:

Stepper motor will become demagnetized, and lose torque over a
period of time.
So I would recommend purchasing a new stepper motor if yours is
over 10 yrs old.

You might expect that answer from a guy who sells stepper motors, but
is this really true? I know magnets lose strength over time, but do
stepper motors need changing every ten years?