Hi SH:
Keyboard is connected to high end computer with high end MIDI interface (M-Audio 2496) and Midi-Ox via good quality Midi cable
As per post #1, the key-bed was removed and the membrane key switches (which are all in perfect condition) were thoroughly and meticulously cleaned by me. All 'note on' and 'aftertouch' behave as expected according to Ox, thus it's highly unlikely the key switches are at fault, as the intermittent strangeness isn't note dependant, sorry if I gave that impression in post #37
Thanks for the Audacity tip, I'll keep it in mind. I admit I'm loosing hope and patience with this keyboard, as did the my mate who gave it to me!
PS: added a camera pic, channel 16 is selected, 5 is an interloper, no midi off!