On my 96. I never noticed that it dimmed before but now it is
stuck dim from the bottom up about 85% to the top. No big deal except that where the transition between normal and dim there is about a 1.5" smudge running the length of the mirror horizontally.

Anyone know whats going on?

The mirror is shot and needs to be replaced to cure the "smudge".

That happened to mine also, the fluid in the mirror leaks out. I found a used one at a place called go-go auto parts, found them from a search of the web. They were great to deal with and I found one already painted the color of my car I think for 35.00.

So I'd need to replace the whole unit. Great, I'm sure there's a ton of
light green metallic's around. There's about 5 other issues to address first.

If you can't find the right color, you could probably do a pretty good job with a spray can of touch up paint. Having said that, I think the glass alone may be replacable. I'd try that route first. maybe a junkyard mirror and just swap the glass.