Do an AS search for gaskets. You'll find the "dollar bill" (new is better) test: close the door or damper on the bill around the gasket. If the bill slips out anywhere, replace the gasket. Do not use larger denominations such as $20.'s; I tore one in half and got yelled at by SWMBO.:bang:
Using the gasket cement ( called "water glass"), use as little as possible. As said, be sure the groove is clean; I use worn chainsaw files, scraping the groove with the file end or tip. If you can, the wire wheel or grinder head can work IF you can get it into the groove ( not possible inside the stove on a damper in a cat stove for example).
Best gaskets are the high density ones from dealers. Cheap big box soft gaskets are not worth the $$$. For older stoves where the surfaces or cast has slightly deformed, use a slightly larger dia. gasket.
For our 2 stoves, gaskets are checked and replaced if needed every late spring when the flues are brushed. I use a "smoke bomb" ( HVAC ) to check the plate seams of both cast stoves.
Messy, but simple job that saves wood and overfiring.