Swan microwave SM2060 tripping RCB

i could use a little help on this fault please.

Firstly i used to be domestic appliance engineer but moved onto high pressure cleaning equipment.
I know the dangers of capacitors storing energy, discharging capacitors etc etc. I used to do a lot of microwaves, but this one has a strange fault.

New swan microwave SM2060W purchased by my daughter .
Used the microwave twice no problem.
Third attempt it tripped the RCD 30mA at the consumer unit.
Tested mains 13 amp fuse in plug, tested ok.
Brought the unit back to my house.
Removed cover, discharged cap, tested main Fuse 8amp on mains board.
Fuse was blown.
Tested insulation of high voltage components, transformer, magnetron,
checked diode, insulation of turntable motor etc.
All tested ok.
Replaced 8 amp fuse on mains board, tested and boiled a jug of water no problem, so took it back to my daughters.

Told her it needed a good test.

Plugged the unit in, no problem controls all powered up, set the power level on the control board to 100{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} and the RCD tripped again.

The start button had not been pressed, just power level selected and the the power tripped, Brought round to my house again , checked it and the fuse on the main board had blown again.

rechecked all insulation etc etc, replaced fuse and works a treat.

Now my house doesnt have RCD whereas my daughters has.

Any one any ideas,

by the way she bought the item from ebay from a seller with a good reputation but is now no longer trading so sending it back as faulty is a no go. That would be too easy, kids dont you just love em!

cheers