I'm curious to learn what other's opinions are on the quality (lubricity, durability, additive package) of the Valvoline full synthetic engine oil. I have been using this in my 1997 Accord EX exclusively since immediately after about a 5K mile break in period as Honda advised me that the enhanced lubricity from this oil would negatively impact engine break in. I have been satisfied with the results so far as I now have 60k miles on the clock.

My doubts arise, however, when considering using this oil in the 300 SDL. I'm very concerned about seal leakage. The car has historically run with conventional Valvoline 10W-30 with 3K mile oil change intervals. Further, with the 3K oil change interval related to, and dictated by ash loading on the oil from diesel combustion, is the conventional/synthetic argument rendered moot?

All opinions appreciated.