This is not an answer on Laurens question, because I do not have the M3W for a long time.
Nevertheless I maybe have and answer how to treat the Centa-rubbers so they keep fresh and flexible.
When sailing - It was our profession for 50 years - we used always glycerine to soften all the rubbers. On a sailing vessel there is a lot of rubber which can dry out, because of the sun and salt.
Every half a year we softened f.i. the window rubbers with glycerine.
Keeping that in mind we have two sets of rubbers for the Centa.
One set we keep in a plastic bag in cloth with glycerine.
We will change the rubbers every year and take the old one out and prepare them with glycerine.
Silicon works too and spraying once in a while is a good idea as a simple maintenance job. But treating the rubbers every year and use a treated spare set will absolutely keep the rubbers fresh
I looked for articles on the web to confirm our experience.
How-to-softening-rubber+ Oils, such as silicone or mineral oil, can help to moisturize and soften the rubber.
+ Rubber softening is the process of restoring hard rubber to its original soft and pliable state. Over time, rubber can become stiff and brittle due to exposure to heat, sunlight, and other environmental factors. This can make the rubber difficult to use and prone to cracking or breaking.
+ using WD40 on rubber can actually cause the rubber to harden and deteriorate over time. This is because WD40 is a petroleum-based product, and petroleum can be harmful to rubber.
+ Glycerine: Glycerine is a natural substance that can soften rubber. It is often used in the production of rubber products and can be applied to hard rubber to restore its flexibility.
Restore-natural-rubber-products+ Pour some ammonia into a pot of warm water and immerse the rubber article in the water for 1 to 2 hours. This will be enough time for the ammonia to evaporate. Follow the directions on the ammonia bottle for guidelines as to how much ammonia to add to the water.
+ Restoring Rubber With Glycerine
Wash and scrub the rubber item until it is clean.
Wrap a wad of cotton in stiff wire that can serve as a handle. A bent coat hanger works well.
Heat up the rubber piece in a pot of boiling water.
Pull the rubber out of the boiling water, then dip the cotton wad into some glycerine, and wipe down the rubber item with it. Let it dry for 24 hours, then heat the rubber again and wipe it down with more glycerine.
