Thanks again for your feedback
@Don_ih - it's appreciated!
I did indeed clean the sticky residue on the blades using oil (after trying with isopropyl, which did not work).
And as you say, the groove where the white "friction sliders" ride in are gummed up and dirty, it would probably be worthwhile to thoroughly clean them and re-grease them, was wondering what to use for this. The sliders have bent metal bands facing the inside of the easel (under the mm-scales), which I think were greased at one time (now just dried up gunk), the other side (under the inch-scales) is just plastic, also somewhat greasy / gummy / dirty).
Also I have realised now that the slim clamp along the top edge not clamping (not lowering down completely, but staying a bit above the baseboard, on it's right half at least) is actually what is keeping the blades themselves from lowering down completely
Thus the horizontal top blade is "lifted up" and not able to lay down nicely.