Nevertheless, I have dealt with this rubber lip with the Sonaxpflegemittel inside and also outside. After initially I was "flabbergasted". The previously hard and deformed rubber lip was within seconds again soft like new, and also the original form was again available.
I use the resources now for the seals around the plastic windows and doors of my apartment - there was the first wear after 10 years already noticeable. And even there, the agent has proven.
Therefore from me a clear recommendation, even if it for the amount (100 ml) initially appears already quite expensive.