You're right...I'm not sure what type of finish is on the stock.
There's quite a bit of it left but, naturally, there are missing spots and wear places.

I've had the buttplate off and the stock is sound. The holes showed up after hunting in the rain with it so I assume they have been there a long time. I was thinking of using AccuGlass to fill the holes and cracks and then smoothing it down to the actual surface. It's tough as nails and blends well with dark colors.