1988 ranger 2.3 starter problem

I have had my ranger (1988) 15 years ,I replaced engine at 6 million miles :grinyes: and all went fine for about 25000 miles and the starter went out. I got a starter at advanced auto ( lifetime warranty) .I now have replaced 5 starters , after about 15 starts the starter will either break the nose off orstrip gear on starter, I have looked at the flywheel and have found no teeth missing . I have heard about it may need shims ,I have never found any loose bolts when checking the starter, Can anyone help ,I have been driving this little truck for a long time and it deserves to be started with the starter not rolling it down hill.
Thanks