I used the Latex-ite crack filler from Home Depot to fill the cracks and the sealer afterwards. I put two coatings of the 10- year sealer. After two winters, the crack filler has broke into pieces and I can see the cracks again. The cracks are about 1/8”-1/4” wide.

Only hot tar can fill your crack the way you want it filled.

I haven't actually done this, but if you get one of those propane camp burners (like the Kiawanis uses for pancake bakes) and a big old pot you can heat the solid tar (if you overheat it can catch fire - don't use water, use dirt) then get some tongs and a coffee can or pot with a handle and pour the cracks. YMMV.

How big are the cracks? For very long and massive cracks, there are contractors who own machines that heat tar and can apply the hot tar where needed.

If hiring such a contractor is out of question, then DIY.

One product is Black Jack concrete patch. You can use a caulking gun to force it into the cracks (clean them first).

I would warm the patch later to make it go all the way down the cracks - but caution : this stuff is highly flammable.

If you can't warm the tar with a torch, do this on a hot day in the summer.

Lowe's carries it.

On flat roofs we use Torch Down Roofing. However even on a hot day (no fun in CA), we need to use a propane gas powered torch. The torch makes the material extremely elastic and adhesive. Hold the torch too long and there starts a fire.