motor oil, water, gasoline, pretty much anything liquid will work in a pinch for brake fluid... a 300D has solid rotors, non vented, kinda makes little sense to use a low boiling point fluid for stopping the car.
5.1 is compatible with fluids used in our cars, and has the highest boiling point yet. it is NOT the silicone dot5 fluid.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!