There are tiny vent holes in the cap for the brake fluid resivoir, plus water can get past the float switch seals. Water & brake fluid is NOT a good recipe; cover up the reservoir.

Found this post/threads while searching this subject. My question is, would it be better to remove the underside shield prior to washing the engine compartment so as to flush everything to the ground rather than on the shield?
Steve

Yes, and you can clean the shield while you're at it. They tend to accumulate a bunch of crud.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References