Have over 300 hours on my 550. I did a valvetrain refresh at 200 hours. New cam follower bearings, timing chain, valve seals, HG, and dual valve springs.
I've done hree waterpump seals aswell. Only had slight coolant leaks.
I dump in some rotella every 5-8 hours, oil filter every third or fourth change, and screw/locknut valve checks at 30 hours. They are very easy to maintain. It's 10-15 minutes to change the oil, and less than an hour to do valve checks.