This thread over on CDF Q asked what causes ring breakage? I'm not sure how true it is but one reply states that engine oil cools pistons but fuel lubes upper cylinder / rings. This is interesting in light of fuel lubricosity of ULSD vs ULSD + TCW3. I just wanted to bring this discussion to everyone's attention.

Well I can speak for the older engines 12V and 24V engines... There shouldn't be any fuel fired till the piston is near TDC. This should fire the fuel into the bowl of the piston so technically there should be very little fuel to cylinder wall contact. Now as for the Common rail and it multi-firing events (pre and post) it really possible... So that does bring up a wear issue...