What is breaking? Frame? Electric motor? Gear teeth?

Just curious. I’ve been repairing some old dead regulators recently by welding new teeth on the gears.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles