My experience with natural rubber and high pH is that the alkalinity dries the rubber out causing premature cracking and leaks. Not sure of the mechanism, but it can and does happen.
At pH 9, you really don't have an issue. I am talking pH 12.5+, and due to strong base like NaOH, KOH. Lime is pretty forgiving for example.
Also, watch out for organics that cause swelling of the rubber!
Hope this helps.