Engine Belt Tensioner And Bolt Issues. Please Help.

[WILLIV]

I have a 2008 mustang v6. I have put some money into to fixing because of the last owner. I replaced the power steering pump, harmonic balancer installed an alluminum thermostat housing replaced all hoses fixed minor interior problems reconnected the radio replaced the cooling fan installed new brakes and rotors. I am stationed in Japan now and my father is looking after my car. He said he noticed my tensioner shaking and wobbling so he took it off to inspect it. He said once he took it off he not that the hole where the bolt goes in was rounded out. He said the bolt goes in just fine but the last two threads on the bolt are worn out possibly from the wobbling. could this be a problem from the old harmonic balancer that was replaced? He said he could find another bolt and get a new tensioner plus a washer to help with the small rounded out open. Will this be a good idea? I'm just curious he says it's fine but he has always worked on his old mustangs and chargers "The original leg spreaders" he calls them. I just need to know of any other ideas. I have found other good tensioners but those are for the GT's in a multiple bold patter and the v6 only has one. I can't put one of those on can I?