Have a circa-1998 Maytag gas dryer (model LDG8410AAW). After cleaning out exhaust vent thoroughly (as well as replacing belt), having problem where the auto dry mode is not working on the timer (the other timed mode, however, does work). Should I replace the timer, or is there a sensor that needs to be replaced?

If the auto dry is not shutting off, you probably need to replace a sensor, not the timer.