For the rear drains in the far corners of the sunroof tray you often need to loosen the caked debris with a long piece of coat hanger wire. Blowing into the drains risks something jamming in the vinyl tubing down at a pinch or bend. Suctioning the loose debris with a long piece of vinyl tubing taped to a vacuum nozzle works well and you can see what you're doing with the sunroof partially open and a good flashlight. An alternative is compressed air back up the drain hoses which end just above the fender drain slits. In sedans you can also access the drain hoses in the corners of the trunk where they join the rear window vent drain tray window hoses. In wagons there's no rear window drain so no point in removing the side panels.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now