Can't remove front element from shutter.

[EdSawyer]

do you have a strap wrench or 2? those can help a lot. Difficult to apply even torque without one, and if you apply uneven torque it distorts things and ironically makes it harder to unscrew. Also, a real heat gun is much hotter and more focused than a hair dryer.

[resummerfield]

...if you apply uneven torque it distorts things and ironically makes it harder to unscrew....

I would echo the advice on the strap wrench. Or, if the front element does not protrude from the barrel, simply set the front barrel down on a rubber sheet or something with friction, and press down to increase the friction while turning. This works the best for me.

Sometimes just gripping the lens barrel with the hands distorts it (makes it into an oval) and will tend to lock the threads.

And don’t forget the heat.