There's no problem for most, though the newer engines are in general somewhat less reliable than the older ones. My [rather limited] experience with C6.6s has been nothing but positive (nothing special about them but they seemed to work fine in machines I run and I've never heard of or seen any common issues with this engine).
XxTrasHxX just happened to be very unlucky, and get a few bad engines with similar problems. That does happen from time to time, though such issues are usually resolved in later model years. For example, many 2006-2007 365CL and 385CL excavators had all sorts of issues. The 2008+ 365s and 385s are in general fine, but of course there are always exceptions, good and bad.
I have never heard of any issues specific to the C6, C6.4, C6.6, or C7 engines from anyone other than XxTrasHxX, so don't worry
. The 320DL is a very nice machine.