Pictures would help but it sounds like you have a post war made replacement stock on your M39. Post war M39 stocks do have a dry, unfinished appearance but they actually do have a finish sealing the wood and its completely normal for them to look that way. Applying anything else to such a stock will seriously devalue the rifle in the eyes of most collectors and I wouldn't recommend it.(I have a very large Finnish collection). Wartime M39 rifle stocks were finished with a mixture called Kiväärintukkiöljy(Rifle Stock oil).The exact recipe is unknown because one of the largest chemical company's in Finland still owns the rights to it and will not share it even though it isn't currently produced. It appears to be a mixture of boiled linseed oil, beeswax, turpentine and possibly bitumen as well, some collectors in Finland have been attempting to recreate it themselves but hadn't quite gotten it right last time I checked.