The ground mod is an excellent one however if you cannot get the parts or are not confident then making sure there is no corrosion inside the Starter motors and bare all the metal where they are supposed to contact will work wonders as per my links.
I have 5 CX/GL500 Starter motors here,all serviced and all spin as if brand new.What I have found is that the carbon brushes are very robust and even the highest mileage starter I have(around 60,000 miles) they are only half way down
