In the last month though, it's been displaying some unusual and troubling behavior.
Normally, with a typical load, it'll finish in about 35-40 minutes, leaving the clothes dry to very very slightly damp (meaning "on the very edge of being 100% dry"). This is using the part of the dial scaled from "less dry" to "more dry" with the setting being just past the first "less dry" tick, which is the setting I always use.
If it's a load full of beach towels and jeans, it might take 50-55 minutes to finish, again with the clothes dry to very very slightly damp.
However, in the past month, the drying cycles seem to be taking about ten minutes more, with comparable loads, than they'd taken before.
More worrisome is the fact that now and then, I'll start it, then come back to it in 45 minutes, and the dryer will be stopped, but the dial will not have moved (i.e., the dial will indicate that the thing is in midcycle). The clothes inside will be hot, so the dryer will definitely have been kicking out heat, but they'll all still be soaked.
I clean the lint filter every time. The exhaust vent has been cleaned out as far as I can get my arm into it. When the dryer is running, the same strong blast of warm moist air can be felt coming from the outside exhaust.
I hope this is enough background so that I can be offered some suggestions of what to check, and what if anything might be wrong.