Call him. You wouldn't have been given the number if it wasn't appropriate.
Consider though that a slipjoint is a very basic design and has a good proven track record of handling abuse over time. It shouldn't need adjustment if properly built for service and Mr. Cover's is one of those. Your slipjoint should give you 50 years of service before wearing out.
Unless you want it to look prettier, there is no need to have it "refurbished." Deep scratches can't really be removed and additional polishing can soften a knife's lines and may not be desirable. A new edge, no matter how carefully applied will change the blade profile. You may want to just keep it and care for it. That being said, I just had a 25 year old knife polished and a new edge put on it by the maker. They would due it for postage, but I sent $30 more anyway. The reason I had the knife refurbished was that the knife had a lot of scratches and it was designed with a mirror polish, it was pretty flat so buffing wouldn't change the lines and it was dull and needed a new edge. I got a prettier and more useful knife back, but you can tell it has been worked on, primarily by the new edge and the deep scratches that couldn't be removed vs. polished surface where there was just light scratches.