It's geek talk:
YW = You're welcome!
HTH = Hope this helps.
High humidity isn't ideal for long-term storage of wine. It can cause labels to become moldy and even fall off the bottles, but I don't think it will damage the wine itself. Not sure about that. Anyway, from what I've read, humidity ideally should be around 60%, +/- 10%.
I'm surprised that the temperature varies that much from top to bottom of your refrigerator, but if that's what the thermometer says, great!
BTW, I noticed one user review on Amazon that said the glass on your unit is not UV resistant. That's a problem for longterm storage of wine -- light can be almost as bad as heat. Think how upholstery and drapers fade in the sunlight. You may want to put the unit in a room that's normally dark, or perhaps get some of that anti-UV film made for windows from your local home improvement store. Aluminum foil would do the trick, too, but it's not as pretty and would block the view of the wine.
As for the 1979 Brunello, whether it's still good or will continue to improve depends on exactly what wine you have -- who made it? 1979 was a good year for Brunello, but not a great year, according to one source in my library.
But contrary to popular belief, wine does NOT improve indefinitely. Except for truly great wines in excellent years, very little red wine lasts more than a decade or two (whites die a much earlier death, but sweet wines may last almost indefinitely). Yes, the flavors marry and mellow and the wine becomes more complex and interesting as it ages, but at the same time the fruit fades, the tannins disappear, the color goes, the nose dies, and eventually all that's left is a dull brown, foul-tasting liquid.
Your bottle of Brunello is already 28 years old, and my guess is that it's unlikely to improve and may in fact be over the hill already. If you have a name, perhaps someone here can provide more information.
HTH, again. Don't hesitate to ask more questions -- wine is nothing without sharing.