If 110v power is available, a heat gun style hair dryer is a great option. It can get hot enough to thaw things out, but usually won't damage plastic etc. Also does not require addition of solvents or oil or graphite to do the thawing. Any or none of those can be added after the key again works.

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