Need some advise .. i have a 1940 chevy pickup . pickup has been coverted to 12volt but i was still running my 6volt starter. Recently the starter went out . I had it rebuilt but advised the shop not to change the teeth or anything else on starter except to make the internal guts 12v. I got it back and now when i start the truck up every other start i get the grinding on flywheel noise . Its hit and miss other times it starts just fine .. is this something that shims will fix ? Im wondering if the rebuilder changed something up on starter that he shouldn’t of or if making it 12volt will make the starter teeth come out futher and now shims would be required? The Help i need is should i start with shims or take starter back to rebuilder to correct the issue ? Why would i need shims now and didnt in the past ? any advise would be appreciated fyi i have tried reajusting starter to bell houseing didnt seem to help and its two bolts so a miss alignment would seem pretty hard to have.