I agree with the comments on regular oil changes, but do you not think its just for our piece of mind?
I had 25 years in motor trade (merc and then vw commercials), and have seen the service intervals creep up and up. But....I`m the same! Its different when its your car and your paying.
But, I have also seen the huge mileages these trucks and vans got with only manufacturers servicing. And they dont have an easy life, I can tell you. And yes, the mercs were chain driven cams (duplex tho). They also use fully synthetic oil.
Way back, a batch of van engines did stretch the chains, but this was down to a poor quality material, and that was the end of it.
My wife has been unfortunate enough to have the dreaded chain problem on her Spider (`08), but as I see it, that should be the end of it...... so long as the new one is of a modified type, including the oil sprayer, if indeed they are modified??