The sunroof drains need to be sorted out, also the OP as a MGZT T estate, so to do the rear sunroof drains click the link below.
https://www.the75andztclub.co.uk/for...5&postcount=27
There are four front drains two on the inner wings, which only drain water down the inside of the front wheel arch liners, and should never let water into the car.
The two plenum drain tubes are passenger side under the ECU and in front of the pollen filter, which can let water into the car through the pollen filter housing.
The drivers side plenum filter which can not be seen is under the servo, and can only be rodded from under the car.
https://www.the75andztclub.co.uk/for...86#post2914186
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Don't forget to do the scuttle panel clips also, and check the EWS as Andy stated, the ECU may have got wet already though.