UGH!!! Starter Issue. HELP!

Id say the gear reduction gear prolly slippin on its shaft (maybe sheared pin?)
Starter shop dont bolt the starter to an engine so this prob wont showup.
However, when bench tested, the gear still has enough "press fit" tightness to make it seem like its workin ok. When bolted to engine it slip, especially if sloppy tolerance cause starter gear to hang up in flywheel> Jus my 2 cents.