The moisture sensor was very clean, so that didn't seem to be the problem. I had just cleaned out the exhaust vents, so that wasn't the problem either. I decided to go ahead and buy a new heating element. Took apart the dryer as per video. It is not very difficult, although there are a lot of steps. Once I got to the heating element I could see clearly that there was a break in the inner heating coil. I installed the new element which was identical to the old one. The only difficulty was that there are two power wires (blue and white) for the two coils of the heating element and I forgot which wire goes to which coil. In fact though, both coils have the same resistance and length and connect to the same point at the other end, so I just guessed. In fact I later found a wiring diagram online and so I think I got it correct. Putting it all back together was easy but takes a little time. Dryer works like new.
I suggest replacing the drum slides at the same time that you replace the heating element, as they both died around the same time on my dryer.