I've repaired my Logitech Trackman Marble a few times over the years, but this time the traditional fix [1] didn't work. But I have seen enough Adrian Black computer repair videos [2] to know that perhaps, a liberal application of DeoxIT Spray Contact Cleaner [3] on the buttons might work. I ordered some last week, and when I went out to check the mail, I found it sitting on top of the mail box! I'm surprised it didn't fall off.
Anyway, a liberal amount of DeoxIT in the buttons and yup, that did the trick this time.
Sweet.
[2] https://www.youtube.com/user/craig1black/videos
[3] https://www.amazon.com/exec/obidos/ASIN/B00006LVEU/conmanlaborat-20