Hoover DYN8164D-80

Hi, some help would be much appreciated if possible…
I am a gas engineer, plumber and electrician (not a white goods engineer)
I’m getting grief from her indoors not being able to put a wash on!
This Hoover washing machine is plugged in on a single, un-switched MK socket with RCD protection at the split board.
The machine is 18 months old and has worked without any problems and no nuisance tripping. About a week ago the RCD tripped and after a process of elimination the washing machine was the culprit. The single socket which is part of the dedicated ring for the kitchen has been tested and found to be satisfactory!
It was pulled out of its housing, unplugged and the rear casing was opened and motor and element tested (ohms), all found to be ok!
It was left for 3 days without being plugged back in, I then went back to it to test it, plugged it in and it did not trip the RCD, wife was happy, she did a wash and thought that might be the end of it (damp wire/connection somewhere in the machine)!
Too good to be true, machine is back to fault status again (as soon as it is plugged in it trips the RCD, machine is always in the off position when doing so!
This leads me to think that the fault must be before any major components and must be with the wiring harness/plug/loom or PCB, that or earth leakage somewhere!
Any suggestions are greatly appreciated!
Mark.