If you look on the fullfatrr forum (yes sorry about that) near the top for "wiki" you can download the workshop manual from a link on there. Sorry to hear about your friend.

At least my back plate wasn't that bad to need 6mm !

One dodge is to use 4mm set screws nylock nuts and washers to replace the retaining pins (and yes it's what I did having tried other options, it works ok)

All most certainly a vacuum leak and it's not like you hear the hiss like an air leak.

First port of call would be battery I think.

Well its an extra 6 volts but still think would be better on the mains !

Couple of Aa batteries in a tens machine are unlikely to give it a shock might need to connect it to the mains to do the trick 😁

Key won't come out ignition unless gear lever is in park, so you sure it's not that a problem there ?

Yes.

Most of them will be off until you start the car, it's not a jeep by the way it's a range rover sport.

Think it's fuse 18 in front fuse box if you pull it and replace it fool's the steering lock ECU and lets you turn the key just once , you could try that see if key will turn.

Had to change tank on mine, the end of sun roof drain pipe wasn't in the sill properly and was touching the tank so water from drain instead of just dripping down was up against the tank and rotted it.

Be better if you had codes read but , steering angle sensor, abs problems for a start.

Yes.

At the risk of spoiling the fun, isn't the 'thinky ' the diverter valve to do with the FBH?

Yes but only needs couple seconds.

Got mine from eBay couple years ago.

Try a battery reset first.

If you remove the strut mark round the nuts on top before undoing them to stand a chance of getting them back in more or less right place.