Waxy gunk coming out of the door drain is Cosmoline (rust preventative) applied during manufacturing. Most of it gets washed off at VPC and ends up inside the door where it seeps out - more so during summer months when it gets hot.
You can use a mild detergent or solvent to clean it off. Just don't let it sit for too long as it'll harden and becomes a pain in the arse to clean it off later.
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Current BMWs - '20 X5 xDrive40i M Sport, '20 BMW M550i | Past BMWs - '03 E39 540iT M Sport, '06 E53 4.8is, '11 E70 M Sport LCI
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