My TI-86 is definitely one of my favorite calculators.

Unfortunately, it's developed the issue with the screen that so many of these older calculators do and about half of the horizontal rows are dead now.

Last I attempted to open it up, if I remember correctly, I saw that the ribbon cable was sandwiched between some glass and a PCB for the display or something like that. In any case, I think they are using some sort of conductive adhesive, and that it is failing, but I cannot actually get to the display end of the ribbon cable.

Any advice on fixing this? I think the TI-86 is one of the top three graphing calculators Texas Instruments has ever built. This is an age related issue, so at some point there's going to be none left that haven't succumbed to this. I'm really hoping there's a fix here so that even if I do mess this one up and end up buying another working TI-86, when that one inevitably goes I'll be able to fix it.

I also own a ti-85 with a couple pixel rows missing and I haven't opened it up but I am hopeful that it might be easier to fix.

Unfortunately yes this is a very common issue, Kerm made a big thread about the 83+ line but it's still relevant for the 85/86 too: https://www.cemetech.net/forum/viewtopic.php?t=5161&start=0

Since OP says it's dead rows rather than dead columns, it's not the same kind of issue- it's more difficult to fix.

If you look at a photo of the TI-86 mainboard, the display driver has two ribbon cables coming off of it- one for rows and one for columns. Those are the equivalent of what's referred to as the "fine ribbon cable" on the 83+ series, where intermittent columns on 83+es are usually issues with the data bus connecting the main CPU to the display driver over the "coarse ribbon cable" (which is the one that's pictured after hand-soldering wires as replacements in the thread tr1p1ea linked).

Since this issue would be with the connections between the display driver chip and the LCD rows, this is a fine ribbon cable issue which is basically impossible to fix unless you have the sort of equipment that's used to manufacture them in the first place.