Bought the AEU1632 and changed it over today. The numbers on the backplate were exactly the same as the existing one (which I had changed about 10 years ago for one from a spare panel I had which was not push button either). The 'new' one now works.
I had already added an extra earth connection from each end of the printed circuit the last time I had a problem.
I had tested the 'new' when it arrived and the resistance readings between the terminal were reasonably as the figures which had been given. Tested the 'old' one taken out today and it seems to be open circuit on two of the three readings which explains why it did not work. No idea how that happens on a unit protected in a dashboard and hardly used though.
There is a dodgy connection somewhere though. The dash backlighting seems to be intermittent dependent on the multi-connector. The connector is on OK but it needs a bit of pushing around by grope to get the lights on, maybe a fault in the printed circuit.