Herb,

We have had several Tower engines at our field that wouldn't shut down and silicone at the carb base as described above did fix the problem.

If you use marvel air tool oil or most other oils you do not need to worry about the carb o-ring or other rubber parts. I fill the carb with oil when closed, open the carb and flip it over many times. O.S. says after run oil does little good unless you use a lot of oil. Most fuel manufactures say their fuel has additives and after run oil is not needed. The most important part is at the end of the day. Disconnect the fuel supply with the glow starter on and make sure all raw fuel is burned out by trying to start.