Could also be some biogunk that, over the years, filtered through the cabin air intake under and in front of the windshield, so you have a clog at the rather coarse filter mesh.

Or in their someplace.

Does the blower motor sound different? Usually, if obstruction on the air intake or output, the fan motor note may rise a bit.

If the fan motor note has dropped, well, perhaps the blower motor lube is finally spent, the contacts between brushes and the on-armature contacts are wearing down, or, well, who know.

Our Uncle Art Benstein has a super swell write up on Volvo 240 HVAC blower motor replacement.

I believe to replacement blower motors exist. One from Siemens and another, well, I dunno.

Please research!

Others may have helpful suggestions coming up in a pinch of the brickboard.

cheers,

Carmex Head.