RE: Smoke in the Turbine duct P-80
I would not worry about it if the smoke is not excessive. If the motor is that old it might be a good time to have some preventative maintanence service done anyway, and they will check all of the internal connections.
You might want to also check the operation of the fuel shutoff valve, you might have some dirt or debris that is preventing it from shutting all of the way. I would swap it out.
But again, if it is only a small bit of smoke I would not worry.
Regards,