If you haven't even started this engine, you don't know if you have an air leak or not. My daddy taught me "never try to fix something... that ain't broke"! Not every engine has this air leak your speaking of. If your engine won't shut off, then and only then, fix the problem. And stop flippin that prop until your ready to crank it. I know it feels neat, we all have done it, but it's not good for the engine. No matter what the fellow at Tower told ya!
Suptter