90% chance its your crank sensor. Heat related. The motor warms up and the crank sensor flames out. It's not disconnecting the batter that brings it back, but rather the engine cooling off. Been there done that with several vehicles of your era.

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1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!