MSR2000 TX problem.

[PETNRDX]

Here is a question for you MSR2000 experts.
I am familiar with most repeaters, especially Micors and a bit less on the MSR, have worked on
a dozen or so of them, but not run into this specific problem.
We have a VHF cont duty MSR repeater that has stuck in TX about a dozen times in about 5 years.
It stuck in TX a couple of times when configured the "Motorola factory" way.
Meaning SCM, TOT and Squelch gate cards only.
Wanted DTMF control and ID, so added an NHRC 4 controller, using the
"connect to the backplane" method leaving the SCM, TOT, AND SG cards in, but using the
NHRC to "drive" SG.
Things were fine for months, then it stuck in TX a couple more times.
Unplugging the station they powering it back up sometimes cleared the fault, sometimes not.
Users can't tell me if the station ID's when it sticks, but I am going to bet it does not.
The question is, is there a common failure in the SCM or TOT card (I know the SG is a piece of :o) that
causes these things to stick?
Obviously the TOT is not working right or it would time out.
And I really think the users would have heard the ID if the problem were coming from RX or the controller.
I am inclined to remove all the cards except SCM and use just that and the NHRC, defeat the SG and TOT
and put the in a drawer.