I've recently bought a high mileage superb with the CFGB Engine code. Now, I've had experience in the past with the oil pump key drive on a seat exeo.

Although all the reports state that this engine code doesn't suffer with this problem. I thought I'd go safe. So after 195000 miles my key was like this. I'd recommend ANY tdi with the balance shaft keyway, change it!! 

2 hour job, £100  incl oil and filter. 

Doesn't look too bad to me for 200K, I think it would still have outlasted the rest of the car.

What is the problem with this key drive and where is it? Never heard of it before

The key drive connects the oil pump to the balance shaft unit in the sump. The key drive wears slowly. When it has worn enough, you lose the drive causing the oil pump to stop. 

The first thing to happen will be the turbo will fail, then you'll get a "low oil pressure ". By then it's too late.