Garage floor under door issues

[Xodium]

This is my first post, so please tell me if this should go somewhere else. I recently moved into a rental and have been working on cleaning up the garage. I really want to seal the door up so I can use this space to work in during the summer months. Anyways, I noticed that the floor was broken up near the bottom of the door and that when the garage door was installed one side is sitting about half an inch shorter than the other side and the concrete is broken uneven across the floor.

Hopefully the pictures explain better what I am dealing with... I attached them to this post.

Is there anyway to fix this so the garage can be sealed properly? I'd prefer not to have to reinstall the garage door entirely, but I will if that's the only option.

 

[James-W]

Several years ago I was at a guy's house who was working on his garage. The concrete under the garage door was pretty much broken up and when the door closed there was a rather large gap on one side. He rented a concrete saw and he sawed out a trench under the door large enough to put a fairly large metal pipe. He put concrete into the trench first and then put in the pipe. Once the pipe was in the trench he made the pipe level with the bottom of the door so when the door closed it sat firmly on the pipe. It worked OK for him, perhaps it would work OK for you too.