The handle on my shower faucet is stripped, the hex screw wore a ridge around the stem. Do I have to replace the whole unit?

Look inside the faucet handle for damage. A cracked handle would need replacing, as it cannot grip the faucet stem. If the ridges inside the handle are worn, the handle cannot connect with the stem and control the faucet.

Inspect the end of the faucet stem for damage. The tip of the stem should have ridges that connect with the ridges inside the faucet handle

single cartridge? pull old one, flush some water through empty valve then install new cartridge. once installed, make sure the horseshoe clip is properly inserted to keep the stem in. once the clip is in right, there is a chrome tube with a ridge that slides over the barrel and the clip. the ridge acts as the stop for the handle. also make sure there are stops inside back of handle to hit the ridge on the chrome tube. the plastic inside the handle may break off allowing the handle to spin. the stem unit/cart may also be installed 180 degrees out of place. pull the lock clip and use the remover tool that came with new cart to rotate it 180 degrees with water supply turned off.

spray spray spraay with wd-40 let sit spray again

your video doesn't show much of your shower for very long, but at a guess i'd say you have separate hot cold taps, in which case always turn on hot first then carefully turn on cold to ensure there's no issue with water pressure. if there no hot water running at all the hot water valve is faulty

drill it out call delta 1-800-345-delta for new handle

hi mike:) do you mean the tiny little hex bolt which holds the tubspout in place or the handle?

You can use any high speed drill bit and drill the set screw out, it should be chrome plated brass, so, it will be soft. If you get your sizing right, maybe, just over the size of hex in set screw, you may be able to save the handle and get the rest of the set screw out. You could also try an "easy out" that will fit in the shole you drill to extract the set screw.

BEHIND THE HANDLE THERE SHOULD BE A SET SCREW THAT HOLDS THE HANDLE ON THE STEM. THE SET SCREW WILL BE BEHIND THE LONGEST PART OF THE HANDLE LOOK AROUND BACK OF THE HANDLE. AFTER REMOVING THE HANDLA THERE WILL BE A STEM AND A NUT THAT HOLDS THE ASSEMBLY IN THE HOUSING

the whole faucet is bad it has an internal leak replace the whole thing

i looked at it and there might be a press in cap with a screw underneath where the grohe label is. there also may be a set screw around the shoulder of the handle where an allen hex wrench fits to losen its clamp on the stem. also.......some handles just snap on and just pull off with some tugging and wiggling them just right.