Clean it up and take the time to apply new gasket material. Acetone works to clean the old adhesive off. Clean as much of the old adhesive off as you can after you remove the old gasket material. Even if you have a non stock door.
As for the door opening, this should go without saying, but attach the gasket material to the barrel of the smoker as opposed to the door itself. I would not waste a lot of time attempting to bend, say, a Cajun Bandit door, or even the stock door.
If it's a Cajun Bandit door well then make sure that the latch is adjusted to give good clamping force.
Below is my heavily modified 22in WSM. Gasket material everywhere that I can put it, it's nearly as tight as the Kamado Joe which stands behind it.
Cajn bandit door, gasket material attached around the door opening, Southco latch clamped down tight, but not too tight.
At the bottom portion of the door opening in the barrel of the WSM, put your gasket material on the inside and along the bottom edge of the opening.
At the lid, place the gasket material at the top edge of the mid section.