I love these Logitech Marble Mouse trackballs, I have one for every computer.  After a few years they slow down physically.  Cleaning the dust off does not help enough, something different needed to be applied.  I’ve been researching lubricants and oils, doing some tests with households; but I think I’ve found the perfect fluid.  Ian Gomes of Union Sound Company made a recommendation a few years back for Penny and Giles faders.  A quick amazon search lead me to Lucas Silicone Shock fluid.  I must report that it is the perfect product for this application.  If you need a drop, I’ll send you a q-tip of it in the mail.