Having a parts car or two also factors into the equation as well. The parts cars are often bought for what one or two of the parts are worth, and the parts can be removed and inspected at your leisure. Still it is often true that if a part is prone to failure at a certain mileage or age it will be bad on a parts car that exceeds those limits as well.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150