Technical Guides for BMW E24, E63, E64, F12, F13.
Follow Tim's great DIY for clearing the drains then if you don't want to have to worry about the front's again create these.
I'm afraid I don't own a convertible so I can't create anything for the rear drains though.
2mm Stainless Steel Mesh
10mm Rubber Edging
0.2mm Marine Grade...