Many years ago, I bought a W110 230, where a PO had replaced the ATE master-cylinder. The replacement had an angular, tilted reservoir, making it impossible to completely top-off the brake fluid. At the time, I also owned an early '70s Audi wagon that had an up-angle tilted ATE master-cylinder - with the older round-style reservoir. So I swapped the reserviors between the two cars, which made both reservoirs appearance & angle perfect.

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DrDKW