ols wives tales
One thing I have learnt is that " seemingly outdated aviation advice" as this wood prop question seems to have been taken, turn out to have very good sound reasons behind them, often obscure to some and nearly always me.
Best in my opinion is to go with the 'general experienced advice' regardless especially if the worst scenario is a bit of bird faeces.
I am sure water penetration of wood props has been decreased over the years with recent coating innovation and timber treatments but if you have to leave the plane outside then covers can be purchased for the blades which may help somewhat but if I had a wood prop it would be at the horizontal position.
I always leave my metal prop horizontal too.
Please make sure the master and mags are off before hand.