I would want to remove any trace of WD40 from the wood. Use a 50/50 mix of BLO and turpentine and 0000 steel wool to clean the wood. After a 24hr drying period and heavy coat of BLO, allow it to stand for 20-30 minutes then wipe it as dry as you can with a clean rag. It well be dry and ready for another coat in 24hrs. The key to getting BLO to dry in one day is to wipe any excess off the wood after a short period.
Google "Gunstock Doctor" and get some Tom's military gunstock wax.