Some progress. I checked the vacuum lines and they all seem ok. I can blow down them and suck down them with one end blocked and they appear to hold air/vacuum ok.

I did discover that there has been a repair into the plastic vacuum reservoir(? what is it for?) on the battery support tray. One of the plastic sockets has come off and been replaced with copper brake pipe. It actually seems pretty good and air tight. I sealed it a little better with super glue. And went for a test drive. Still no joy, though the cruise did engage once, which is once more than it ever has!

So a few questions:

Does the Cruise Control servo ever fail and are there any tests for it?

I have seen a picture with a 1 way check valve on the cruise control vacuum line, think that might help?

And in a different area I have heard someone mention the brake light switch, and testing by pulling up on the pedal when setting the cruise - surely if the brake switch was sticking on the brake lights would be on all the time or am I missing something?