Two out of my 3 MX900s have the goo. They were low use trade ins from a house I did a few years ago. I also have a 980 that has this issue as well as a trade in Harmony that has done nothing but sit in my desk drawer for the last 5 years. I also have an MX850 that has been in constant use for almost a decade. The back of the remote is shiny and black, never had the goo issue.

A few weeks ago I fired up a pair of MX850s for a client that had been sitting in a box for a few years. Both have this problem.

It almost seems like lack of use causes it. All of the above remotes had periods of disuse, all were stored inside climate controlled spaces.