Starter symptoms started this spring when I noticed starter was sluggish to turn over on occasion and then occurred more frequently. Most recently I turned key and starter motor spins but starter pinion does not engage/deploy. Noticed if I have ignition on and jump solenoid while applying slight preasure on rear of pinion assembly it will deploy but starter barely turns over. Had battery charger on motor and charger indicates battery is good. Any thoughts on how to further diagnose appreciated.