All that to say yes, a TVS that failed would get very hot. Between the diagrams you can validate but definitely sounds like the normal failure.
What list of issues cause TVS failures Vernon ?
I have the Rev L fully updated. I've run it for a half dozen years with 2 Z1000s on fixed 1 and 2 on two seperate loops.
I have noticed the side near the red indicator light getting fairly warm through the vents when running engines with a combined 8 motors or more on the two loops.
Since I know the jumbo Lionel and MTH transformers and our little Lionel Power Max 40w all have cooling fans I figured the TIU , not really a transformer but a controller of sorts , would benefit from some sort of fan.