My daily driver is a '06 TDI Jetta and there have been a fairly large number of camshaft failures attributed to the
zinc being removed from some of the diesel spec oils that VW requires. I use ZDDP in that, but am switching to a high
zinc (1400ppm)
synthetic Rotella CJ-4 spec
oil. There are many threads and thousands of posts on the tdi forum regarding
oil analysis, chemistry, base stocks, on and on. The consensus is a Patrick suggests- much over 1600 ppm is not any additional benefit.
170K miles on mine so far and the camshaft is still in good shape.