Every time I get ready to fill the water in the tub, you can see the water going down slowly and eventually if I wait around too long my water will be drained all out from my tub. I have a little chip on the outer part on the metal part, it's not the part that you lift. The maintenance guy at my apartment complex keeps saying that there is nothing wrong, when there is clearly a problem. Is there something to put over the drain or a sealer?

I'd say do the test yourself first. Fill to a certain level and ut a piece of tape at the water line. Find out how long you have to wait for it to drain 1/4".

Have the maintenance guy come over and watch and time.

The seal isn't made in the drain, it's made in the pipe. The flipper plate comes off and you can pull the bell up and there is an adjustment there. It's tricky to get right.

Some flat stoppers MAY work for you. It depends on the contour of the tub.

Do the test and report back with your findings. Hopefully, someone will post a picture of the mechanism.

A video how to do it is here: How to Fix a Bathtub Drain Stopper | Video | Tub | Bathrooms | This Old House