Bleach is the safest cleaner to use for aquariums. It breaks down very quickly into water and is easy to clean out.
The seals on the other hand are a different matter. Seals that have algae growing underneath them are on their way out. Its possible that the tank could last another 5 to 10 years, but imho
its safest to just redo the seals. Its not a difficult job by any means, just takes a bit of elbow grease.