I took my luggage rack off to clean it a few months ago. Before I replaced it
I put screen in the four drain holes to keep leaf litter and the like from
sitting on my roof. I simply cut small squares of metal screen, pushed them
into the hole from the underside (convexed on top to prevent clogging) and
hot glued around them. This has significantly reduced the amount of crap
sitting on (staining) the roof and and running down the windshield after a
heavy rain. The rack still drains very well, however, you do have to grab a
handful of debris out of it every now and again.

Nate Richmond
'83 Westy "Merriweather"