You might try some Wurth Rubber Conditioner (spray can) & let it set 24-48 to soak in some, or another brand rubber conditioner (non-silicone). Wipe off excess when done soaking it, & put it on some sheet plastic to contain the mess/overspray.
Wurth also has an applicator stick version, but that's more for coating smaller seals while installed on a car, & you'll want to take your main seal off to treat it on all sides with lotsa product, so buy 2 cans (they're smallish).
You can order Wurth products from TC'sGarage.com & maybe some of the other Porsche & Euro parts places (maybe BavAuto.com).
Tom
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