Wood Fitz grips were available both finished and unfinished, with the logic being that the unfinished grips wouldn't shift and slip in a sweaty hand. The maker of the Fitz grips (John Paul Jones) was somewhat local to me and I exchanged a number of e-mails with him about his grips before his passing, and I ended buying his last remaining supply of "Gunfighter" style N-Frame grips, several of which were unfinished and look like what you describe, dry and dull... so, are you sure yours were originally finished?
Over the years I've used Tung oil, Tru-oil, Min-wax antique oil finish and I've settled on Permalyn gun stock finish from Laurel Mountain Forge:
Finish,
Peramalyn
Gun Stock Finish,
4 ounces,
by Laurel Mountain Forge - Track of the Wolf
I've begun using the sealer version, which is thinner and penetrates better, but it take a lot more applications to build up the coats to get the sheen desired... in exchange for better control of the outcome. A very easy product to work with.
Can you post some pics?