Tiger I Heavy Tank 1942-45 describes the results a test of the automotive lifespan: a first production series Tiger was used. Before the test it was run-in for 25 km. After 52 km a blockage occurred in the steering gear. The engine was replaced several times and it ended the test with its fourth engine, having covered 7736 km. Whether any other things were replaced isn't mentioned however. (because nothing else was?)
During use in combat mechanical lifespan is usually much worse than during testing I've read, so the question remains.