A4 brake problems

2001 A4, 1.9TDI 130. Done about 80k miles...
About 3 weeks ago, was driving home, when suddenly the brake pedal became very spongey. Shortly after this I lost all servo assistance.
Came back after about 10-15 seconds, but then went again after about 3 brake applications.
Drove home at 15mph with hazards on (was only a couple of miles from home) and got Audi Roadside out. Technician said he thought it was the vacuum pump, and got it towed to the local Audi dealer.
Got it back just over a week later (having had an A6 as a loan car), within 24 hours it went again. Got it recovered again, this time they replaced the brake servo. Still faulty, so they replaced the master cylinder.
Meanwhile, on the way home the night before I picked it up, the brakes failed in the loan car (A3 Sportback 2.0 TDI). Got this one recovered, picked mine up... which had failed again by the time I got it home.
So got mine recovered again, they replaced the ABS pump. Picked it up the following afternoon, and it failed again halfway home.
Drove it back to the dealer (carefully - the brakes were working a bit better so I was able to drive it back) having phoned ahead. They got their head technician out, I had a quick chat with him and took him out for a drive in it to demonstrate the problem. (Hitting the brakes 3 times in less than 2 seconds, while not a natural braking pattern, would cause the fault to present itself.)
He then said to try dropping to 2nd and floor it. Which I did. His response: "Did that feel a bit sluggish?" Which, I have to admit, it did a little. His response... "waste gate".
So we drove back to the dealer, and he explained that he thought the wastegate may be sticking open, which would cause the vacuum system to lose pressure. Which does make sense, but what do you lot think?
It's gone back in now, am currently waiting for a call, hoping to get it back today...
--
Glenn Richards Tel: (01453) 845735
Squirrel Solutions http://www.squirrelsolutions.co.uk /
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Glenn Richards wrote:

Update to this saga (if anyone's been reading), I got it back, drove to London (about 2 hours drive from here)... and the brakes failed again.
So I've traded it in for a newer one, Same engine (1.9 TDI 130), same colour, but the Quattro version.
--
Glenn Richards Tel: (01453) 845735
Squirrel Solutions http://www.squirrelsolutions.co.uk /
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