Broken starter gear

[rayfinseats]

Ok, so this all started with a dead Walmart battery, dragging, hard to start. Timing was a little high so I backed it off to about 4 degrees BTDC. Stock 350/4 bbl.

SO I go to walmart and they test the battery and it's bad so I get a new battery. 650 CCA. Same problem, hard starting. I get a rebuilt starter. Still hard starting. I solder the battery cable on the starter end and replace the batt cable end. Ground is new and solid. Grounds to block and body etc. Started fine before all this.

Tried rebuilt starter with/without one shim and new starter with no shims. I've never had to shim a starter before on a SBC.

SO I go buy a "new" starter. With a charger hooked up it started fine so I figure I had problem solved. Next day grinding somewhat again. The flywheel looks good. Anyway today the starter gear BROKE. ANy ideas WTF is going on here. 83 chevy k10 stagered bolt starter. 168 tooth? TH350 trans.
Should I replace the starter and add shims till the dragging sound stops?