Turbo issues/cylinder oil leak

[showbiz]

Long time no post! Hope everyone is doing well.. Grab yourself a cuppa before you start!

I started writing this a few weeks back but now, armed with more information, I am hoping for a better response given what I now know!

Car is a 2006/06 wagon with the 2.0TDi BKP engine. Done about 170k miles, 80k with us and about 75k with a Superchips Bluefin map (not turned up to the max, to protect the DSG). I look after it on the driveway and I'm happy to tackle most jobs!

Just a little over two years ago, we had issues with limp mode; first intermittent (every few weeks) until it was undriveable about 3-4 weeks later. I fiddled about a bit, cleared codes (VCDS), changed the thrust sensor, some other faffing and eventually sent the turbo to Midland who rebuilt it for me (at a very reasonable price). Car ran great, a bit smoky when booted but I put that down to the remap and it was greatly improved by the refreshed turbo. In the last two years it's had a cam belt, oil pump drive upgrade, new downpipe/cat, several oil changes and a collision with a Belgian Caddy van which required a new HID headlight, which wrote it off.. Anyway.. Two years on and we're in the same boat - limp mode and the turbo is back with Midland. They called today and said the veins are sticky and there is a carbon build up on the piston shaft which could be letting oil from the turbo into the exhaust, and they are going to do a (very reasonably priced) strip and clean.

So, my question is, how has this happened in only 2 years? The car has done about 18k, a large percentage of which has been on the motorway (wife does 80-160 miles a week on the M20) and a few fully loaded trips to popular holiday destinations, but it's not been raced or rallied! When I removed the turbo, I noticed one exhaust port on the block was wet (well, damp, when the others are dry) so my theory is an oil leak into that cylinder, but I don't really know where to start looking and I've been told it's unlikely to be low compression (piston rings) that is letting oil through, so it could be something on the top end? It had the injectors done during the recall, but could it be a seal? Or a glow plug seal? When I noticed this, the car had been sitting, on jack stands, with no engine oil in it, for about 2 weeks.

Any direction greatly appreciated - sorry for the long post but I wanted to get it all down! The wife wants it back ASAP - she's driving a relatives Volvo XC70 2.5T at the moment and hasn't been impressed by the extra cost of fuel!