Actually I agree with you that synthetic is overkill. But I use it anyway and
change it every 3000 miles. There is a lot of proof out there that the best
thing you can do is to consider changing it more often with a "normal oil"
(every 2000 miles)

I am an old air (cooled) head at heart this being my first water boxer and
still try to use the best. (I make my wife shop at K-mart however--) oil
doesn't "do it all" in the water boxer and you have more room for error.

Actually for a diesel I would go with a high detergent diesel oil. Find out
what Mac trucks recommends.

Todd T
84 Westy
Washington DC