Can you post pictures?

It's not easy to do right now, I'm away from my eqpt. since I'm at the inlaws' but I will try.

I looked again this morning and it seems the first thing that happens is the leaf turns evenly dark but the veins are still green. Not splotchy but evenly dark over the entire leaf except for the veins, which when you hold it up to the light are still green. Then they turn crispy brown and curl up dead.

Test post - photos of tree

I haven't figured out how to get photos to display here but this is a gallery of 5 photos of the entire tree, upper half closer up, a pic of the darkened sick leaves, and another pic of more advanced leaf damage that also shows some unaffected leaves on the same branch. I hope ths helps.

I don't think your link is working.

Many of the species are subject to wood rot and decay. Take a stick and give the trunks a whack. If you hear a hollow "thunk", be prepared to have them (it) taken down eventually.

I had two massive old lindens (not littleleaf) taken down two summers ago. They were pretty hollow.

FAIL! LOL

I'll have to try again later, time to drive to MO.