Colt will no longer do repairs on the older models.
Finding a qualified Colt pistolsmith these days is tough.
Too may of todays gunsmiths just don't understand the old Colt design and it's common to get a Colt back with more problems then when you took it in.
Grant Cunningham is good, but he's backed up at least several years and he only opens his waiting list every couple of years:
Cylinder & Slide Shop are a top custom shop with a good reputation for Colt repairs.
As a top shop, prices are high and turnaround is slow, but quality of repairs is high: