Thanks, MG, for those numbers. I've known for quite a while that my guitar was valuable, and have sometimes thought of getting an appraisal, but no one is selling it anytime soon -- not while I'm alive -- so why bother?

It might bear mentioning that my D-18 was made early enough in '69 to feature the old Brazilian rosewood back and sides. Martin had to switch to some other slightly-less-desirable variety of rosewood later that year.

My pickguard started to curl up a year or so ago; I've hit it with a hair dryer and peeled it off, and am about to install a replacement. I'm thinking of ordering a tortoiseshell pickguard (from Martin) instead of the original black, just for the hell of it, along with a set of tortoise-and-white bridge pins. Would this reduce the value? (Such "changes" wouldn't hardly be permanent, of course.)

What about having an under-the-bridge pickup installed? On the one hand, it would be an "improivement"; on the other hand, it makes the instrument less "original" from a collectors-item point of view. Any opinions? (I'll do it anyway if and when I can afford it.)