soft floor, depression under bike wheel, oil guard?

According to my trusted RV tech, toyhauler garages seem to be vulnerable to leaks at the bottom of the rear door/ramp and around the door. He told me when looking at used toyhaulers to check the walls for soft spots near the door and to thoroughly check the floor for soft spots starting at the back door and at least three feet into the garage.

I suspect that you are looking at replacing part of your floor.