Thanks nctnico.
I am very pleased with the outcome, a working E4421B! In my dreams I did not think to get this magnificent generator for so little money (relatively speaking)! Yes all levels and all frequencies appear excellent as measured on a Siglent spec-an + FA-3 counter. This thing is beastly good. it reeks quality. So far its life was 34,400 approx hours, 200 power ups, with lcd being on for 100% of the time. It must have been in a factory or long running in an assembly line or similar. I have turned on screen "light and text saver" and see a difference slowly coming. Even then LCD and backlight is good, maybe a slight yellowing.
I was able to win an eBay replacement reference module (same as mine, same xtal unit) that is on the way. So I can see if that is better or worse from my doctored one when it arrives. Also then it might allow some experimenting with changing the xtal to a OCXO. CCT seems to be able to cope with many differing mountings and types, sine-square etc. Only thing is if xtal is oven controlled I am not sure how it will react without enabling the "oven cold cct" (5 minute timer) in software, as I don't have any confidence/knowledge (treading carefully) in any software changing, yet!
Very chuffed I got a working good generator.
On any repair, "Never give up, never surrender! (Galaxy Quest)".
Minsik.