Disassembled the steering wheel controls yesterday.
Had to remove the horn/airbag with 3x #6 octagonal screws in the back. Careful not to get killed by the airbag - you'd have to be quite clumsy/unlucky but unplug battery if you're worried.
Leave the selespeed paddles alone, if present.
Then carefully pull out the plastic buttons towards the centre. This silver plastic trim is stupidly fragile. With age, it might as well be made of thin glass. They are held by 2 clips towards the centre of the steering wheel.
Then the circuit board is revealed, using standard microswitches. Apparently the issue was smudge on the circuit, causing a short on exposed wires. The board is being worn with friction, and wires become exposed - I guess. Cleaning up and bit and issue was resolved and customer is happy.
NB: With afterthought I should probably have put sealant on the exposed wires so it won't happen again. Oops