You can do a few quick things, add a new external spring, literally a spring by drilling two small holes or a coupling as aforementioned, but if air motor is indeed still good only, most of time it is just weak or too long.
The tension of the spring is the real problem not the bushing. Unless you feel or see an exhaust leak trace?
FYI
Bushing for loose appearing point is there cold but as the cast expands due to heat becomes tight.
So you have exhaust leak trace?
If you had aviation turbo prop experience at altitude changes for a bootstrapping, you would understand real fast since in planes we monitor temp in each cylinder and the turbo plus manually adjust a mixture for this.