As a Scubapro trained repair technician - I can't complete the overhaul of a regulator set without evaluating IP and cracking pressure. Without bench testing the reg - I have no idea if the first stage and second stage are tuned to specifications. In training - it was emphasized that both guages (IP and magnahelic) are required for adequate testing. Without disparaging the shop in question, I'd encourage you to utilize the services of a shop which demonstrates professionalism and thoroughness in their service procedures.
Rinsing and soaking in warm fresh water is a fantastic idea after every dive in salt water. It makes the service technician's job easier. However, even mineralized fresh water may leave a scale. And salt water will certainly leave deposits that are difficult to remove with rinsing or vinegar. Time in an ultrasonic cleaner with an appropriate solvent (e.g. GMC's hydosonic cleaner) are important in that they return the parts to a factory clean state without damaging the parts and removing chrome. I'm unaware of any dremel tool attachment or abrasive that will perform a similar job. Nor was one recommended during my equipment clinic. Perhaps the cost of a professional grade ultrasonic cleaner ($600) and solvent ($29+$30 hazmat charge) has something to do with their tool choice?