Definitely don't use WD40 on your camera. That has a thin solvent, with a gloopy component dissolved in it, so that once the thin stuff dries, you're left with thick gloop in your device.
I guess you're trying to free the focusing? If so, the solvent I would try first is lighter-fuel, which is not much different from petrol. Here (in the uk) I can buy this in Swan brand at a tobacco kiosk - I have to ask for it, it isn't displayed (because it's hazardous, unlike everything else they sell, which is all totally safe!) It comes in a tin with a little folding spout at the top, whcih is good for dispensing it in small quantities.
Your lens is supposed to focus just with the front element turning, so you don't need to go near that rear element. You can probably do this without removing the lens/shutter unit from the camera. I would put one or two drops of solvent at a time onto the screw-thread behind that distance scale. Put the camera on something like a towel, and that on a tray or something, so that any of the solvent that drips or drains down does no damage to your table.
If you see the old grease dissolving and running down, it's probably best to wipe this away as you see it.
Leave it for a while to let the solvent penetrate. This is going to be slow: the solvent has been evaporating from the old grease for decades after all. Be prepared to keep putting on a tiny amount of solvent every few hours, for days.
Every now and then, try twisting the front element. To apply serious force, you might consider a pair of grips, lined with rubber or leather to stop them from scarring the metal.
If you get the front element turning, exercise it back and forth, and maybe try adding a tiny bit of new grease to the thread, on the end of a matchstick or a toothpick. I use ordinary grease - the same that I use on my bicycle bearings.
I see the camera is currently focused at infinity. You could try running a film through it before trying to free it, as long as you don't try any close-ups.
The part that is touching the sides when you fold the camera - is it the hooked lever near the bottom - about eight o'clock when you look from the front? If so, that's the shutter release. There should be a linkage from the release button on the camera body that presses that; I can't see it in the picture.
You could turn the whole shutter unit a little to avoid the lever from touching the frame: you'd need to loosen it's retaining ring inside the camera - slightly tricky. But anyway it looks to me as if it's correctly aligned now (with 'AGFA' at the top, if the camera is held vertical). If the shutter release is working now, then I'd try to live with it how it is, rather than risk an adjustment that stops it working.
Good luck!