Flooring – How to dust proof and waterproof garage concrete screed

Carefully determine where the wheels of the bottom of your door stop being used. Any point below the bottom of the wheels when the door is completely down should be safe to remove. The track shouldn't have to go all the way to the ground.

I would not paint the track, for fear that it will interfere with smooth motion. If anything I'd use grease to lube up the track, which will put a protective surface on the inside of the track where you need it and improve performance (less resistance).

Rust on the outside of the track won't matter except aesthetically.

From the description and photograph, it appears that the crack is the natural result of the sort of stresses one would expect at a location with:

• Drastic change in slab width to extend the slab through the door opening.

• Drastic change in thermal stress where the slab transitions from interior temperatures to exterior temperatures.

• Drastic change in slab stiffness. Dynamic vehicle loads are applied sequentially from the rigidly supported portion directly above the wall below to the spanning portion where they create deflection in the supporting structure.

All of which is to say that repairing the joint does not mean filling it in. There will always be a joint there. Instead, repairing the joint probably consists of keeping water out using backer rod and a flexible traffic sealant rated for wide joints...and perhaps a metal joint cover.

There's no magic in a can that it going to defy the laws of physics or change the internal stresses of a concrete slab under dynamic vehicular loads. Any repair needs to be premised on acceptance that there will be a joint across the opening where the slab narrows.