I suspect the micro switch on my existing Honeywell v4043 zone valve has
gone bad.

I have a new Honeywell v4043 motorised zone valve. I was using the
valves manual lever to test the existing, it never seems to start the
boiler when in the "MAN OPEN" position. Examining the way the manual
level works on the new valve I note that the paddle never quite reaches
the micro switch.

Is my new valve duff as well? Should manually moving the lever to the
"MAN OPEN" position cause the micro switch to be activated and the
bolier to fire?