Hello!
2 issues mixed in - Aging and death by execution. The original question asked about how much pain a TVC can take before it gives up and dies. As far as aging goes samplesj summed it up nicely - the TVC itself does not wear at all with time - no moving parts at all. The switch used to select output taps will have a life of some kind. The shallco I used much of the time for that has a life of a minimum of 50,000 full ccw to cw rotation cycles. The high quality sealed relays used in the TAP boards have a min life of 1 billion cycles - not million but billion...... That's a lot of volume adjustments...... I use that same part on all TAP boards - TVC boards, Resistor Boards, Source select boards, etc....