As far as what causes premature failure, oil feed and drain line inspection/cleaning, refusal to prime turbos before first start, the biggest one is no proper boost leak check and going full send with 100% WGDC and figuring out the details later. Boost leak related problems are probably one of the most common issues I deal with. Not only do you need to perform one, you need to test the whole pressurized system, and you need to use enough pressure to make the test actually worth calling it a test vs. motherhood & apple pie (yay she held 3 psi, send it!).
There are lots of things that can present as failed turbos (read that: smoke) that aren't. PCV issues especially as these cars get older, jacked up drain lines, and then of course injectors going out can look like smoking turbos, although usually they're accompanied with some fuel related codes when that happens -not always. Actually almost thought my own turbos were going to give up the ghost on my project car, which I expected given what I've put them through. Nope, new index 12's later zero smoke, still going strong 35k in.
IMO the biggest issue really is a lack of a methodical approach to working on cars. Anyone can loosen and tighten bolts, a logical approach and some fundamentals when turning wrenches really helps maximize success with these projects. Especially for the inexperienced, I recommend slow slow slow. No hero time quotes, slow it all down and enjoy the bus ride once. Slow is smooth and smooth is fast. There is nothing magical about installing turbos, it just needs to be done correctly. Same as injectors, etc. etc.
Chris
