Since horn-block off seals are no longer available (NLA), I was able to fashion a similar replacement using a pre-1968 Bus rear window seal. I chose a Kombi seal from West Coast Metric as it was the smallest and cheapest to buy. I cut it to length, then used super glue to reattach the ends, creating a circular seal. A single Bus rear window seal provides enough material for 2-3 seals. I used the opportunity to replace my horn plate with a nicer one, which I stripped, primed, and painted with a spray can of colormatched paint from my local auto paint store. I found it easiest to install the plate into the seal first, then install the complete plate and seal into the body from inside the trunk. Slide your drain hose through the drain plate hole and you are done.