I think I should jump in here since I am on my 4th turbo. Original turbo had 75k on it(or so) when the variable veins stuck and the turbo oversped destroying the bearing. Threw a code for overspeed. A simple fix for this would have been the easy off oven cleaner cleaning like I do to my TDI's. If I only knew then what I know now.
1st replacement turbo had 75k(or so) on it when I had it installed and had only the slightest play on the mainshaft. This one ended up blowing the seal and droping out 3 qts of oil(or so) from the crankcase. No idiot lite, no code, just got LOUD
2nd replacement turbo had "low miles" on it and also had only the slightest mainshaft play when I had it installed. This one never oversped, developed an oil leak or anything. It simply started making loud noise. I just had it replaced this week and inspection shows that the shaft bearing is SHOT and the turbine contacted the housing bigtime.
3rd replacement turbo is a BRAND NEW garrett. I only have about three hundred miles on it so far......so we will see!
My rig. 06 CRD bought new in 06
Amsoil 5w40 since 5k miles
Amsoil oil filter since new, twice a year.
Been changing oil once a yr (12k miles) and the filter every 6 mos.(6k miles) NOT ANYMORE!!
Run B-100 6mos a year dino the other 6
86k on the clock now
My recommendations:
Change oil every 5k
Once a year, do the easy off turbo cleaning procedure.
Let your turbo warm up and cool down EVERY TIME IT RUNS
Dont baby it, blow the carbon out once a week or more.
LISTEN FOR LOUD OR STRANGE NOISES COMING FROM THE ENGINE BAY AND SHUT IT OFF IMMEDIATLY IF YOU DO. TRAIN THE DRIVER TO LISTEN FOR WEIRD NOISES. My wife actually called me last month and told me the turbo "went again" so she can recognise the warning signs.
If you can swing it, go with a GDE turbo. I just could not afford it. Garrett should be ashamed that they dont offer a replacement cartridge so these things can be rebuilt after thet turbine contacts the housing.
Sorry for being so long winded

Bubba