Had water ingress on drivers side. Sometimes all the gears on the LED light up P,N,D,2,3,4 all lit up and the car refuses to shift past 3rd.

VAG suggests it is the shift solenoid. If I clear the fault it goes away for some days but eventually comes back. Sometimes a reboot also clears the problem.

Are the shift solenoids expensive to replace or is this a "right my car off" new ECU?

Had water ingress on drivers side. Sometimes all the gears on the LED light up P,N,D,2,3,4 all lit up and the car refuses to shift past 3rd.

VAG suggests it is the shift solenoid. If I clear the fault it goes away for some days but eventually comes back. Sometimes a reboot also clears the problem.

Are the shift solenoids expensive to replace or is this a "right my car off" new ECU?

The automatic box ECU is on driver side, in a plastic tub under the carpet. If you've had water in there there is a good chance the ECU or the cabling is damaged; you could inspect the cables and the connectors. The boxes are I guess supposed to be water tight (though like the rest of VAG cars water tight is a bit of a loose definition!)

OK. How easy is it to get too ie. do I have to get the seat out? If so, is there a document on how to do this somewhere?

Vagcom fault is as follows:

17137 Shift Solenoid 1 (n88) Circuit Failure.

Is it expensive to replace the Gearbox ECU?

just had my shift solenoid replaced due to all lights coming on and getting intermittent selection of drive, cost just over £100 for solenoid plus extra for fitting