If it's a call that does not have any sentimental value or monetary value you have several options. If it's an important call, you may want to consider sending it to one of us call makers and have us do it for you.
To do it yourself I would recommend an oil based aerosol spray can. Use masking tape to cover the bottom of the paddle and the top of the rails. This is not what I personally use, but my finish tends to be a bit glossy like wet glass. You can also consider using the wipe on polys like tru oil, minwax or watco.. Mylands sanding sealer is something that we commonly use if we want to use a sanding sealer. I don't think you need it, I rarely use it myself.
"Instruments of Mass Destruction"