I believe the best thing to do is replace it. Otherwise I would suggest something gentle like simple dish soap.
There are different types of liquids available for this purpose. You can use those liquids and you can get them from different super stores. It is always better to clean it if you're not facing any problem. But in a case, you're facing some problem then you should replace it.
The following link can also help you about it.
www.kemper.eu
The following link can also help you about it.
www.kemper.eu