Still drooping - so I got underneath yesterday inbetween the snow and checked the height sensors.
On the front drivers corner that droops there was a nut (now I know where it went when I was doing the engine refresh and dropped it!) jammed against the connector, forcing it slightly outwards. I took the connector off and sprayed electrical contact cleaner in both sides. Then I worked it on and off quite a bit and then let it all dry before popping back togther. However this morning - drooping again!
I think I need to get one of those EAS cables - the OBDII to Serial/USB type - I have the EAS Unlock software already. At least I should be able to see if the height sensor is giving the wrong height reading I guess? I don't supose it matters which one I get off the Bay of E?
Tomorrow I'll change the rear brake pads as they are a bit squeaky now.... oh the joy of the P38!