its very normal - make sure the plastic sheet that are behind the door cards are intact - the original ones are extreme cheap quality - you can do better with 6 mil plastic from home depot/lowes/ace

get some body cavity wax spray and spray it inside the door chassis to prevent water from stalling, the wax makes the water slide off and MB applied lots of the stuff on these cars from the factory. Over time it wears off and flakes - reapply it - its not expensive either and it prevents rusting out.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)