whirlpool dryer blowing thermal fuse repeatedly

My whirlpool dryer was running poorly when I moved into new house (needing multiple cycles to dry). I cleaned massive amounts of lint from a very long (30 plus feet) vent run, which solved the problem for a while (2 plus months). The dryer then stopped heating. I replaced the high limit and the thermal fuse. The dryer worked again for several weeks, but recently blew the thermal fuse again. High limit is still showing zero ohms. I checked the vents, and they are still clear. The heating element is not shorted to the frame. The cycling thermostat cycles on the stove top, opening when hot. I don’t know the exact temp. Any thoughts on what might be blowing the thermal fuse? The dryer is 12 years old, but I was hoping to get a few more years out of it. Any guidance would be very much appreciated.