First of all, the game uses 10 "big" boards with many LEDs per board called "WOZ1 through WOZ10" and these are pricey to purchase outright so JJP does an exchange where they send a board to you, you sent yours back and then instead of that being free like it was under warranty, you pay an exchange fee plus the shipping. So it's, for example, $60 or so depending on the big board. The small boards, there are 31 commonly called GIs although they are not all general illuminatiion, are the ones most often swapped. Within a single WOZ these boards are identical save for the metal mounting bracket orientation. These are where there have been more failures (many more) than with the big boards. These can be bought outright or, again, there is an exchange program setup and that fee is typically $20. You can cut a bracket off a GI 29 board, for example, and spin it to orient it however you need (there are three styles, left center and right). So that's basically that, except that from generation to generation there are slightly different revisions of boards. The first (give or take) 500 WOZ machines built use a +5v DC lighting system (and a switching style lighting power supply), then the majority built use a 7.5v LED setup (there are slight variations but it's all workable), then machines built from Christmas of 2016 forward use the new WOZ 2.0 LEDs, a system loosely based on the setup in the Hobbit, although in actuality it is much closer to the setup in Dialed In!. This LED system has proven to be super reliable and will, of course, be installed in every WOZ built going forward as well. The license was renewed so WOZ will be going back on the line soon and continue to be built (only standards and rubies of course; ECLEs were finished years ago) with 2.0LEDs going forward.
The word "buffered" is thrown around a lot and that simply refers to whether or not the boards have small daughter boards added to them (of course later revisions have the buffers built in by the manufacturer) that help to absorb power spikes and shocks (hence buffer) and prevent them going forward on the lighting chain. This was a fix (along with the switch to 7.5v) for the boards causing one another to fail going down the chain. The one great weakness of the initial system is that they are daisy chained together ala Christmas lights, so that one big or small board failure darkens everything downstream (this is NOT the case with version 2.0, Hobbit, DI or any future game). You can bypass one bad board and turn it off in game settings and the game will continue to function sans that one board until you replace it. The software also compensates to try to bring the colors into correct alignment downstream.
I should also note that plans are still going forward in the development of a (it has no name yet officially) "2.0 retro-fit kit" which will allow earlier WOZs with any LED system other than 2.0 to be upgraded to 2.0, thus ending the LED hassle (hopefully) going forward. The major obstacle to this has been cost and the difficulty of doing the changeover, but it is coming relatively soon from what I know. Several customers will no doubt opt to purchase it, although many may not, I'm not entirely sure myself. Look for an announcement about that kit hopefully in the not-too-distant future as the engineering team has been hard at work developing it for months and months now.
Hope that helps you out a bit.