The blue rebound adjustment knob on top of the right fork will not turn. Do these freeze up if they are not turned or lubed for some time? Could it just be jammed because someone turned it too tight? Any suggestions?

Also, there's a small slot head screw in the bolt at the bottom of the fork. This is the bolt that holds the tube and damper assemble in. What's the purpose of this screw?.

This happened to me on a Gas Gas that I bought, don't know if they are the same on the Montesa. Adjusters work by slots clicking on a tiny ball bearing which is spring loaded by, yes you guessed it a tiny spring. On my bike the spring was jammed up with gunk, a tiny grub screw in the side of fork leg top nut is undone to get at this - I had fork legs out as was replacing oil as well.

As for the small screw at bottom of leg, I think this can be used to drain legs - pump out old oil.

Got the rebound adjuster free with some penetrating oil and pliers. Probably too many pressure washings.