Be careful unblocking the sun roof drains. You could knock the tubes off, good idea to clean them out though. If you want to check for boot leaks have one inside the closed boot and one outside with a hose and start from the lower surfaces and work your way up. Take all the affected trim out and dry it fully - it will promote rust if left damp. I had to do my lamp gaskets too.
Good - Fast - Cheap: Pick any two.
E23 735i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E30 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i