my1998tdi wrote:
Again we used either rotella t6 or Castrol Syntec, as we have in all of our tdi's.
Are you sure it was 10w30? T6 is 5w40. Syntec also comes in 5w40 as well. I think 0w40 is fine if you have ORM, GDE, or your EGR fell off/welded itself shut mysteriously... 5w40 if you still run your EGR is probably a good idea. I have spoken with many people in person with CRD's who have run 0w40 since new, and still have their EGR enabled. Not saying I agree or would do it myself, but the last guy I spoke with, yesterday, in State College, PA had 140K on his running 0w40. I had spoken with a fellow in Delaware who had around 175K, same story. Regardless, that valve breaking sucks.
My theory on the valve breaking: A sticky valve (for whatever reason) leads to the piston "tapping into" the valve occasionally, which weakens it. Eventually it breaks. I have seen it in some other diesel engines. What causes it? Could be soot, could be a broken glow plug tip (not in your case though), could be overheating of that cylinder from excessive fuel, etc., clogged air filter, etc. Is there any evidence of the valve "kissing" the piston tops on any of the other cylinders that you can see?