What year did they become factory installed? Is there a way to tell if an older machine has been upgraded with the redesigned sticks?
None too soon, IMO.
Not sure I understand your question? Bobcat has offered SJC controls for over 10yrs (IIRC)....I do know that the new M series machines have an "improved" joystick control. The new machines joysticks have something like 15 more degrees of movement that is very noticeable. When running our T190 w/SJC (which operates great imo) for a while, then jumping into our new M series machine w/SJC its very noticeable...the new SJC is smoother, and easier to make finite movements at WOT.
From digging through forums and speaking with the local service dept. what I've gathered is the early (I think) pre2006 sticks had a round base. These are the ones with the most frequent problems. When they start acting up you must upgrade to the newer style improved setup which runs about $2k in parts. (These have square bases, come with new sticks, wiring, controller etc.). It think there may have been another change in 2008 but I'm not certain on that one. And apparently the new M's, like you said, have been modified as well. The local service guy made it seem like as long as the machine has square based sticks I can be relatively at ease?
Based on what I know, your "local service guy" is giving you good information.