The finish problem is unfortunately common. Over the past several years Martin has been experimenting with different formulas for their lacquers. These dull areas of the back or even the sides, where the skin makes contact are the result of body chemicals (sweat, etc.) making contact with the finish. There is absolutely nothing you can do that will bring back the shine to those areas, and I personally think it would be a big mistake to use any further compounds on it in an attempt to do so. You could end up doing even more cosmetic damage to it then what's there. I had this happen to me with a new OOO-28Eric Clapton (which I've since sold) and also with a custom Martin I ordered a few years ago. It in no way affects the playability, or sound of the instrument nor the resale value. You have to live with it. I'd suggest draping a piece of soft flannel over the top area of the guitar where the arm rests, so that the skin doesn't make contact, and to always give it a good wipe down after each playing session.

Keep in mind that Martin is generally pretty slow to respond to change. They knew for 50 years that applying nitrocellulose laquer on the top finish and right over the pickguard would cause extreme shrinkage of the pickguard and the wood below, resulting in the infamous "pickguard crack" so prevalent on pre-1980s Martins. It wasn't until after decades of this coomon anomaly that they woke up and started gluing the pickguards on, over top of the dried finish, virtually eliminating this problem.

Very recently they had to recall over 3,000 instruments of all makes and models and redo the finishes. This recall has really messed up delivery times on custom and dealer ordered instruments to the point that the average wait time for something is a year to 20 months. Has a lot of dealers and buyers really pissed and impatient. It was a determining factor for my not deciding to order yet another custom instrument.