So, after 31 years, I took a close look at a log wall that has been exposed on the Southwest side, where it get as much abuse from the elements as possible, and here is what I found: Out of eight horizontal runs of Perma-Chink, only one showed any indication of age. This was course number 5 and is the one directly under the 32' tie log that runs above the fireplace, where the interaction of the stonework to the log wall can sometimes cause the log to 'hang up' and not fully settle. This was confirmed by looking at the dovetail corner notch, where there had been some separation. Even though Energy Seal was not yet available, the caulking originally used there was still in good shape and there was no danger of air or water infiltration on the dovetail notch that sloped away from the home. Even with all of that, the Perma-Chink separation was less than 1/16th of an inch, and in that one run only, the other seven runs were still providing a perfect airtight and watertight seal.
The surface seemed to be slightly faded, so I got out my Frog tape and taped the lower edges of the chink spaces (because I am not as meticulous with a brush as most people) and proceeded to refresh the surface of the chinking with Chink Paint. Twenty minutes later, the surface on that wall was like new and I am looking forward to answering the question again at the next trade show with: "I don't know, we've only been using it for 37 years and if you want to refresh the color or change the color, a little Chink Paint will quickly get your home as good as new."