The seals are not that hard to replace. It varies by models so make sure you're looking at the directions for what yo have. Since you may have to remove the toilet from the floor, it's a good time to do all maintenance on the toilet. Think about replacing the floor seals, replace any "O" rings, inspect all parts and replace if worn and generally a thorough cleaning. I'm not a big fan on removing the toilet so when I do, everything is getting the once over.
If the current issue is just a very slow loss of water, you may be able to just rejuvenate the seal with one of those RV toilet seal conditioner liquids. They serve to condition and lubricate the seal and work pretty well on those slow leaks.
Good luck!