I tried to respond to your request about the type of rubber washers but I couldn’t get that particular Q&A posting to provide me with a place to respond. I’m not sure what I’m doing wrong and why I can’t respond, so forgive me for starting this other thread.
For reference, the original conversation is here: https://vexforum.com/t/answered-r7-c-and-use-of-rubber-washers/35301/1
To answer your question about my question, an example of the rubber washer we happened to be looking at is here: http://www.mcmaster.com/#90130A009
But there is nothing special about that particular type of rubber, as far as I know. We could easily use other types of materials, if that were allowed. Also, the fact this is a “sealing” washer makes no difference to us, either. It just so happened to be the one they bought.
Thanks very much for your kind consideration regarding this.