1984 Ford F250 Starter

Dear experts, I have a brand new re-built starter that worked well for a couple of months, then started to stick and keep on running after the engine was turned off. It then worked well for a while. Now it just clicks while trying to start the truck. The batteries are brand new. I crawled under and smelled ozone around the starter. Before I put another starter in, is there anything else I should check on the starter that could be adjusted to make it work? Thanks, Mike
P.S. The trucks has a 6.9 L Diesel engine