Hi
They are usually quite reliable machines, so I wouldn't worry about retrofitting at this stage. I would suspect that the phasing is out on the electrics. What you need to search for on line is the Bridgeport Interact Milling Machine Mk 2 Maintenance manual as it has information in it about checking the phasing. I only have a copy for the Mk1 machine but suspect the procedure is similar if you want a copy.
Regards
Andrew