Toilet Seal Leaking

First.....

Turn off water supply
Hold toilet ball open
Then using your hands...YES your hands.....thoroughly clean seal with dishsoap flexing it while cleaning...top/bottom. Use a flat wood stick (popcicle/tongue depressor) to scrape any stuff off (scale/TP etc)
Clean the ball also.
Then rinse it and dry with paper towel

Using your hands (AGAIN).....thoroughly lube it up with some olive oil (or plumbers grease) really work it in


IF that does make seal work..........hold water
THEN replace it
That probably will mean complete removal of toilet

Just look up your model number .....find part number and goggle it

Dometic (SeaLand) Toilets

FYI
After NINE years of use, I had to use the provided "Toilet Seal Cleaning Gift Pack" that came with my legacy SeaLand toilet.
Includes an abrasive cleaning tool (like a big nail file) and gel cleaner to scrub the area around the seal which solved the leaking problem. Lot of gunk/scale under the rim. I also use Thetford Toilet Seal lube 1-2 times a year when the RV goes into storage.

Maybe this will aid you.

Yes they can be replaced look on you tube tons of videos on how