A/C not cold pre-FL MY09 RS

[K1W1]

Is this a common problem? I'd really like to get to the bottom of it...

I have no idea but if the AC controller is getting incorrect temperature information there is no way it's ever going to work consistentaly and you seem to have had everything else checked.
You said

Dad's RS A/C is intermittent - some days it's freezing cold, other days it just doesn't want to get cold at all and just blows warm air.

if the system had a leak it would never get cold. The fact it gets hold and cold but not correctly indicates to me that the problem is more likely to be electronic than mechanical.

[RaceBlueRS]

I have an 07 build RS. My air con died twice within the last 5 months. The first time they said they found nothing wrong, except it was a little low on gas. They also said they'd put some die in it so they could "find the leak next time"

It died again two weeks before the warranty ran out. They regassed it again. Again they said they couldn't find any leak.

My outside air temp indicator always displays correctly.