I have had work done by most of the gunsmiths recommended above over the last 25 years in this hobby and agree with all of the recommendations. One man that has not been mentioned that should be is JJ Perodeau in Oklahoma. JJ is a fully trained European gunsmith who not only works on many fine shotguns but also many double rifles which is unique. He also turns work around much more quickly than many other smiths. Here is his website: https://jjperodeau.com

As to the issue at hand, I now have every newly purchased gun stripped and cleaned by my local gunsmith unless I have bought it from a shop that has already done so prior to marketing the gun.