Thaks Dave - should have been clearer - none of them need diaphragms / they all need something more major (eg a piece of the internal housing, or repair of an electrical fault).
I just repaired an airtech 80, it had blown its diaphragms and one of the electromagnets was shafted. Thats all there is to them apart from the armature with the magnets in the middle. Cost me £100 but i couldnt afford a new pump (£200) i bought new diaphragms and electromagnets. Seems to be fine so far...
Would appear that there is life in my EL-100 after all. If I move the magnet and then switch on, it flies to the side where I have a split diaphragm and then stops. Not sure if this is because I activated the auto-stop or not, does not appear to do much.
So, have to assume I need a new diaphragm and a new magnet (no idea why a magnet should 'fail' but as they have replacement instructions I guess they do) - but what I really need is someone who knows what the auto-stop actually does so that I can confirm my diagnosis.
Hopefully Jules will have some news after talking to the distributor today.