H W Machine Repair of Fort Wayne Indiana frequently have this sort of trouble refitting the quill to Bridgeport mills they overhaul. Their solution is to fit a wrap of fine abrasive paper to a rubber plunger and drive that up and down the bore of the housing to break the vertical wear marks it has developed in the housing in use over a long period of time. They continue with the process until the quill begins to fit, it can take some time to get to that stage

They finish the job with Time Saver lapping compound to give a smooth shake free fit of the two components, clean the job up and oil the surfaces well as they rebuild the machine.

These are professional solutions to the problem of restoring the machine to original specification.

Brian

If you are able to identify the hard spot what about cutting it away with an abrasive disc on a Dremel type drill. Never tried it myself though.