Don't use WD-40, I know from experience h:

I'd go with something thicker, I personally use gel lube (forget the brand) that I got at a department store for most things like door hinges, etc. because it seems to stay in place and hold up over time far better than thin, messy crap like wd40.

It does take a while to penetrate compared with thinner products (and may not be able to penetrate some things) but for most applications I prefer it.

Keep in mind I've never really used it on a window (yet) to lube the tracks but I'm sure it would at least work better than wd40.

However, I don't know what adverse affect it might have on the rubber in the channels since it's petroleum based. What isn't, right

The only other thing that comes to mind would be grease, but again I can't speak from experience.

I'm not really sure if those channels are lubed from the factory or not (might just be a coating after they're removed from mold) but if they are I'm assuming it's something silicone based so that might be a safer/more effective way to go.