The last link seems to be the real issue... I didn't mention it, but I had tried a search, but only came up with the first three links.
After doing some additional research, I spoke to someone with more knowledge than myself. Turns out it is a BUG in Mavericks. And many others have reported it to Apple via BugReporter, but so far nothing has been done.
Apple basically broke ntpd timekeeping in Mavericks by introducing pacemaker that is *supposed* to work in conjunction with ntpd. Well, it's not. The longer you leave the computer on, the more it drifts, and it could drift a little or a lot, depending on the inherent inaccuracy of your logic board oscillator, which is used to provide ticks. They are cheap crystal oscillators; some run fast, some slow, some a lot, some a little. ntpd takes all this into account by measuring your clock's inaccuracy (it's "drift"), and using this calculation to slew your clock towards the correct time.
Apple's idea had something to do with preserving (extending) battery life for laptops. Pacemaker is supposed to read that drift that ntpd calculates, and use it to step the clock at regular intervals that back off on some sort of algorithm, but it ends up forcing ntpd to stop polling its time source, so the computer starts losing track of any correct time. Nobody (including Apple) seems to fully understand how pacemaker is affecting ntpd.
Most of the "solutions" you mentioned are attempts at solving it, but none of them work in the long run. Only the last link (Clock runs slow when I leave iMac on all the time) seems to have the right idea of replacing the Mavericks ntpd with one from Mountain Lion, also disabling pacemaker.
