My 1974 GMC 4108 still had the original rubber on all but (I think) one of the bay doors. That's 4 decades of use on the rubber.
True, the new rubber is not as good as the old, but it works and will likely outlive your use of the bus. In my book there is no need to switch technologies if the current one is working.
The one thing that I've seen though that can eat through rubber hinges fast, like it did on my 4106, is a bent or warped door. If the door edge and the body are not parallel then the hinge is going to be under much more stress at some point. Check your doors for straightness and adjust as needed before reinstalling.