Most failures on these mainframes are blown pass transistors, rather than lytic caps.
I have 4 TM500 frames of various sizes. I can’t remember how many times I’ve replaced those pass transistors I’m some of them. Sometimes they seem to blow on their own and other times it was clearly a failed plugin.
I always felt it was a weak point in the overall system design of the modular interface approach.
Never have needed to replace caps in the frame.