6. To make an “O-ring” I use a rubber band and coil it around the motor shaft. I then put a small piece of electrical tape around the coiled rubber, so it doesn't uncoil itself. Each layer of the rubber band should be flush with all the others, so the ring can sit flat on the lid. See the images for a clear understanding of this step. Don't be discouraged, this is by far the most difficult part of the build. Take your time to get it right. Make a few coils if you have extra parts and try each one to see which works best.
7. Test fit the “o-ring” by applying petroleum jelly to the tip of the motor shaft and inserting it into the center of the rubber band coil. This will take a little bit of work. The rubber can be quite difficult to work through without enough lubrication. Keep applying the jelly and inserting the shaft. It should slide in with a little resistance but not so much that the shaft will get stuck. If the coiled rubber band is securely taped then you can test the fit by running the motor while it is lubricated and inserted into the center of the rubber band “o-ring”. See pictures for helpful details. If the shaft can still spin even while you hold the rubber coil in place then that is a good fit.
PRO TIP: Try putting some petroleum jelly into a oral syringe (See image) and squirting the petroleum jelly into the center of the rubber band coil. This will also be helpful later to add more lubricant as necessary.