Some useful sites in case you havn,t visited so far.
Most recommended source is cousinesuk.
Yes manufacturers recommend routine M/S replacement. Manual winding gives you an idea how well the spring feels, to say the least eliminates selfwinding mech form diagnostic guestimation.
This rubber has been vulcanised so should be extremely durable and should need little more than a basic clean with water; perhaps with a small amount of detergent.
If the watch has had a hard life and you feel the bezel is looking tired you could restore its shine with a product designed for such rubber such as the 'tyre shine' type products normally used on cars e.g. Meguiars Endurance Tyre Gel or ArmorAll Extreme Tyre Shine Gel.