Hi,
I leave my inner/lower sash track unpainted, but shellacked. The outer track (upper sash) gets painted. The entire parting bead lower half gets painted, but the upper half left natural+shellac.
If you pre-paint the sash and the painted track with oil enamel, there is no need for wd40(ORLY?) but it's safe to use wax; either paste/furniture wax or paraffin if something sticks. Never use acrylic/latex on sash, they will stick in the summer.
Although I never tried it on sash, I think that the Ben Moore "Advance" paint is okey-dokey and although it's water cleanup, it cures so hard that it's free from any sticking problems, and it's probably the wave of the future in any case.
HTH
Casey

Thanks! I could tell something was there, but didn't know what it was. The Idea was not to paint the track of the lower sash. The tracks next to where the sashes sit when closed have never been painted. The only part I'm stripping is above the lower sash on the interior.

I will look into the BM paint. The outer 1/4" on each side of the sashes (front and back) have never been painted and the window is almost 100 yrs old. I like the idea of having something there on the exterior side.

I would recommend a mixture of Boiled Linseed oil and Turpentine. The mixture is sometimes called Bloturp or Blopentine. It will treat and protect the raw wood and prevent drying out. It's a 50/50 mix and apply your mix liberally especially at open grain...let sit for a few minutes then wipe off the excess with a paper towel or rag.

If you get Pure Gum Spirits of Turpentine it will have less of a smell than your standard turpentine. Some variation add 20% penetrol (40%/40%20%) to the mix to add penetration into the wood. I've also seen formulas that add bees wax to the mix. Let it dry and if desired you can wax the jambs with a hard bees wax.

Be careful as rags with oil can ignite if balled up and thrown in the trash. Spray with water and let sit out to dry.

I wouldn't use WD 40 on anything nor would I store it in my home.

WD-40 is great for spraying on wet ignition points. But I prefer liquid wench as a lubricant. ;)
Casey