The the seal loses its shape and doesn't exert pressure on the mating surface, you get a leak.
If it splits, perishes or flakes, you get a leak. So you can either replace them or look after them.
Looking after them with a 5 minute job every 6 months can save you loads of money in the long run.
Especially on a Roadster where water ingress can damage electrics, ruin carpets and speakers.
Offering your rubber seals a hamburger won't do anything, they need proper rubber care food.
Don't be tempted to use any old spray can of something you have at hand, these can dry rubber out.
There are a load of products on the market, I chose Gummi Pflege Stift by 1Z which was bought on eBay. (I hope you are plagued by the Gummy Bears tune like I am every time I see the bottle).
The bottle has a foam topped applicator like the bottles of shoe polish you used to buy.
This is the seal before "pflege-ing". It looks hungry. Give ALL the seals a good wipe
down with warm water. This lifts the dirt from the seal to allow better application
of the treatment, plus it stops the applicator getting dirty.
Pop the top off of the bottle and apply the foam applicator with a bit of pressure to ALL the seals.
The rubber care solution flows into the applicator and you simply wipe it over all of the seals.
Repeat every 6 months to keep the seals happy.
It is even possible that an application of this fluid will restore the seals slightly which could
reduce or stop any leaking that you are experiencing already. For the price, it's well worth a try.
1Z Gummi Pflege Stift,
Wurth Rubber Care,
Autoglym Vinyl & Rubber Care.
If you find any more, let me know.