I was using my computers when all of a sudden, I couldn't select anything with the mouse. My intial reaction was well, there goes the other PS/2-to-USB converter, but some subsequent experiments proved to me that wasn't the case—I could still move the mouse pointer, and the middle and right mouse buttons worked. It was just the left mouse button that no longer functioned.
I have a Logitech Trackman Marble from the 90s (it's not the same as what is being sold today as the Trackman Marble), and it's the second such unit I've used. The first one wore out and I had to go to Ebay to find a replacement a few years ago, I liked it that much. The thought that I would have to go through that trouble yet again filled me with dread.
In the meantime, I couldn't effectively use my computers. As Bunny and I were scambling to find a replacement mouse at Chez Boca, I decided to crack open the Trackman and see what might be the issue. It was easy enough to open, remove four screws and the innards were exposed. My initial thought was that the left mouse button (which gets the most use) had worn out. It was, but not in the way I expected. There's a portion of the button you press that activates the switch below it. It's a small vertical piece of plastic that pushes down on the horizontally oriented switch. And in that small vertical piece a groove had formed over the years of use.
After discussing the problem with Bunny, the solution we came up with was to use a small amount of Elmer's Glue (applied with a toothpick) to fill in the groove that had formed.
I want to report that the solution worked wonderfully! The Elmer's Glue hardened enough to make the left button work and if it ever wears out, I know how to fix it.