Depending on the physical size of your hands, dexterity and strength, it IS possible to remove and replace the heater fan assembly without pulling the dash. The motor is clamped down with a split housing and 2 (maybe 3?) small hex-head bolts. I didn't believe it was possible until a member with really large hands insisted that he'd done it. So I tried it- and did manage to get the fan out entirely by touch while laying on my back! Then a day or two later I put it back- accidentally reversed- and had to do it all over again....
All 12v DC motors in these cars use brushes and those do wear. Given that there's only a very few things that can go wrong with fractional-horsepower DC motors, it's likely yours either needs brushes or lube in the bushings. IF you can R & R it. And if you get stuck, well- there are directions for partially pulling the dash and thus finishing the fan motor removal.