alnico magnets lose field strength over time?

[mhanc]

i have read that drivers using alnico magnets lose significant field strength over time. the reason given is way beyond my technical understanding but had to do with alnico magnets needing to maintain very precise positioning in the assembly - something nearly impossible over time given the mechanical movement of the unit.

any piece of gear i acquire is for the extreme long-haul... till death do us part. so, longevity is a primary consideration.

is this something others' are familiar with and can confirm?