Upvc seals leaching black marks

Hi when I wash my windows the black rubber seal is leaving black marks on the cloth and subsequently the white upvc frame.
I understand it's about 20 years old so it's obviously started to perish but it still feels soft and flexible . Is there anything I could put on the rubber seal to stop it giving off black stuff ?

Unfortunatelty there is no product i know of . These types of rubber seals are an absolute nightmare! You can spend more time cleaning the black mark off then the main window . We've never really found an easy way to do it , other than try and avoid the rubber