"...The middle joint with the cork is almost impossible and the bottom just slides on and of...."
If that is the case, then one of the following:
1. You need a decent cork grease such as Alisyn or Doctor Slick
2. The cork needs to be sanded a little thinner. Far easier to do before you get cork grease on it. But do not sand the body material!
3. The body material itself is jamming, in which case it needs to be turned down slightly.
I think there are good engineering reasons why O-rings are an inferior idea for use on tenons. If the joint is to be taken apart regularly, then the rings need lubrication, but retain it very poorly. By comparison, cork is a wonderful material.
But perhaps there exists some elastomer O-rings of a material that incorporates Molybdenum firmly attached to its molecules, as a lubricant. Something like the self-lubricating formulations of nylon, which are unsuitable here because they are not elastomers.
If so, I have not come across it yet.