I would say it is more age related, I've seen this appear on lots of late 80's and early 90's Audis and VW's.
The only proper solution is to have it all removed and have a bodyshop spray on new sealant with a "schultz" type spray gun.
Companies like " Wurth" make this type of sealant, it might be worth asking them if they have a DIY option like an Aerosol Can that could be used for localised repairs.
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