OK, time for an update. I've said the below in other words, in other posts, and in other threads, at least a couple of dozen times before, but hesitate to cut and paste a reply because it's easier to just rewrite it than to search for an appropriate post, copy and paste, and then delete inapplicable parts and add other parts that would make it more specific and applicable to the situation at hand.
Rickenbacker instruments are finished with a catalyzing material called "conversion varnish", generically when referring to furniture and wood finishes. It is a type of two-part catalyzing polyurethane. It is much tougher than any lacquer, and requires specialized equipment and training to use properly. The learning curve on this stuff is pretty steep, and with the investment in spray equipment of a certain type, the necessity for absolute cleanliness, and the amount of labor it takes to spray, flatten, and then rub out and buff the final clear varnish coats, it's no wonder that few luthiers have taken it up.
Were in a period when many guitar finishers and luthiers have come up through the ranks refinishing Fender instruments, using nitrocellulose lacquer. This stuff is easy to mix and spray, has a fast drying time, and is very easy to buff out and get looking good--at first. And it will wear and patina very nicely. But it's not the best thing for fretboards, fretted or not. Everyone has seen a nitro-finished maple Fender fretboard with ten years of hard playing on it, and how nasty it looks. OK, you're welcome to call it "mojo". But it's the opposite of what most manufacturers want in terms of finish performance. Rickenbacker realized this back in '59 when they began using catalyzing finishes of their instruments. Most of the luthiers that you'll meet will have had some experience with nitro; not all are comfortable with even this stuff and approach refinishing as a sort of black art, and consider it the least fun part of their work. Refinishers may be very good at what they do, and may be able to do a super fine job of repainting a Strat with nitro, or French-polishing an old Gibson mandolin, but again, conversion varnish is more than most want to take on as a material.
So, whoever the luthier is that you're considering for the work of refinishing the fretboard on a fretless Rick bass, I'll be willing to wager that he:
Has never worked with conversion varnish, and is not about to learn (80% chance); or,
Has tried to work with conversion varnish once or twice, and gave up because in the end it gave him too much grief (19.99%).
In either case, you will be told that nitro is just as good, and will look great, too. My response to this is: No, it's not "just as good", and, "you haven't seen anything until you've seen a properly applied, flatted, and buffed-out conversion varnish finish. Period."
My saying that it was "easy" was a bit disingenuous on my part; it is definitely easier than refinishing a fretted Rckenbacker fingerboard, which will drive that 99.99% group of luthiers around the twist completely.
I've got several Rick fretless basses in for different kinds of work; the conversion varnish finish on these fretboards is elegant, gorgeous, and very durable. Darned near bulletproof, in fact. Nitro simply will not hold up on these, whether you use round wounds (aarrggghhhh!!!) or flats (aaahhhh....).
