The yellow plastic oil dipstick cap top on my Briggs and Stratton Bolens 500 push mower is on way too tight. I can't loosen it by either hand or wrench. Short of blasting, what would you recommend?

Are you turning it in the proper direction ?

Check the Oil in a Small Engine | Briggs & Stratton Videos (http://www.briggsandstratton.com/us/en/support/videos/push-mower-engines/checking-the-oil-in-your-briggs-and-stratton-engine)