I recently had the wiper grilles and centre panel off. I also rebuilt the rusted hinge pockets.

On my 85, there was no debris under the grilles or in the centre section. Just a bit dusty. There are two large drains that discharge from that area into the engine bay at firewall. Should be easy enough to check that those drains are not blocked by pouring water in. And at same time check interior of car to make sure some of the water is not leaking through firewall.

The hinge pockets have drains that discharge sideways into the engine bay through the inner fender wall. Again easy to check by pouring some water in. On my car the hinge pockets were rusted on both sides down in the vee.This allowed water to go through cabin side wall into the car footwells and likely was main cause of floorpan rust. The outer hole just discharged inside the enclosed section of the fender behind the wheel well. That is also where water that runs down off the windshield goes, in the corners.

I see the hinge pockets as being the major problem area. I kind of neglected the 300D over the years, but I usually try and vacuum leaves out of my cars once a year. The worst ones we get are when we are in SC in the Spring. Don't know what those trees are, but small nickel sized leave fall and are harder to get out than our large oak and maple leaves.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5