If you seal it, I would use shellac. While I've been recommending it for years on various projects (without scientific evidence), FineWoodworking recently published a moisture test rating shellac finishes above all others except polyurethane. Now, this was not a submersion test, but rather light moisture and humidity. It bested varnishes, lacquer, linseed oils, and other poly/phenolic-oils (danish, tung, trueoil, etc.).
Do all your sanding first, then you might use Zinser's Bullseye shellac. I say that brand because you can get it nearly anywhere - Ace, True Value, Home Depot, etc. Using denatured alcohol, cut it 50/50 (in a seperate little container) and apply a nice coat inside the forearm. Wait about 10 minutes and then another coat, and then another. When that has dried for several hours, take some 00 steel wool (or a grey nylon pad) and buff ALL of the shellac off. Repeat the process but not the buffing. After letting that final (6th) coat dry overnight, then buff it ALL off again and apply a coat or three of the shellac uncut - straight from the can. When that drys, buff it witht he steel wool to a nice sheen and you're ready to go. Remember, when you're buffing ALL that shellac off, you're leaving the shellac in the pores and setting it up for subsequent coats - the buffing is an important step.
Another beauty of shellac is that it can be used under ANY finish (poly, varnish, Watco oils, etc.etc). It's a great sealer if you want to use another finish. Just do the first step (3 coats of 50/50) buffed off completely, then use whatever you wanted to finish with. Some might argue that poly-oils are meant to penetrate the surface, but I'm here to say they still will, at least until they hit the shellac wash coat. The wash coat has already penetrated.....