Ah I forgot about the eccentric adjustment. I bought the bike used with a lot of miles on it and it would make sense that the chain has stretched. Now I am also wondering if the sprocket teeth are also worn. The chain replacement is a gimme but the sprockets are much more involved.. I am going to do some googling to see if I can find out how to check for sprocket tooth wear.
Meantime, back to my original statement, I would like to buy the most durable chain I can find. I see that the teeth are much thinner than the main sprocket body. I have a micrometer, are there any go, no-go widths of the teeth or is the wear more prominent in the curveature shape of the tooth ?