Let's start with a 2.0T with 105K, a stuck engine caused by a frozen inlet balance shaft and three codes:
P164b Oil pressure switch malfunction
P0011 Intake camshaft retard setpoint not reached
P0299 turbo underboost

So, I start by replacing the balance shaft, timing chain, tensioner and button everything back up and the car runs wonderfully and apart from the puddle of oil from the front timing chain cover and the three Check engine codes, life is wonderful!
But is it? I accelerate to 3000rpm and the ECM light comes on. I attach an oil pressure tester. The oil pressure is below specs at idle and at 3700rpm.
idle - 1.2 - 2bar (spec is 17.4 - 29)psi mine reads 14psi
2000rpm - 1.6 -2.2bar (spec is 23 - 31.9)psi mine reads 29psi
3700rpm - 3.0 - 4.0bar (spec is 43 - 58)psi mine reads 38psi

So, I go back in and straighten the timing cover, plaster it with RTV black. I take the sump off and check there's no sludge or blockage . There isn't.
I replace the oil control valve. I replace the blue regular oil pressure switch. I change the low pressure brown switch for good measure.
I test both switches and verify that they switch at the correct pressure. I check the circuits for continuity to both and everything is fine.
Before I run my next test I attack the P0299 code. I pressure test the intake piping. I spray all the joints with soapy water but don't see any leaks.
I replace the N75 valve (the one that pulls on the Wastegate) just for good measure.

Here we go again. I button it all back up and go for a run. ECM triggers at 3500rpm just like before.
I come back with the same three error codes and an oil puddle from the front timing cover. Is this getting irritating or what?!!!

I promise my wife I'll never buy a cheap Audi again and open it all back up. I pull the sump, remove the oil pump, take a look at this frustrating piece of ***#@$! and go in for dinner.

OK, now I have a new oil pump on order, but I don't want to come back in a fourth time. I'm assuming the camshaft code is simply because there's not enough oil pressure to operate the camshaft adjuster thingy.

1. Is it worth taking off whatever it is that sits above the oil pump and checking on my crankshaft bearings?
2. How the hec does this stupid lower timing chain cover seal? Really? Can it be that hard to make a timing cover that seals properly?
3. Is it worth simply replacing the turbo while I have everything apart? The car has 105K. Maybe I should replace the engine with the one from my BMW 540i It gives me no grief!!

Of course I could stick a black piece of tape over the check engine light and one over the ECM light and drive around with an unregistered car because I can't pass emissions in my state.
I'm amazed that with so much effort I still can't beat this machine into submission!!

So, all that ranting, in the hope that someone can shed some insight or tell me to hang up my wrenches and go work in the yard.

Mark