I've used both BLO and PTO on my Garands. Prefer the BLO finish but as mentioned earlier, PTO for water resistance.
WD-40 isn't a good cleaner, lube or a wood preservative. There are much better (and recommended) options for both wood and metal, especially on the Garand's moving parts.
http://www.garandgear.com/cleaning-y...grease-your-m1