I can't really tell what parts 17 and 18 are. Here is a photo of what I have, on the shaft in order. I have replaced all the orings I could see, but maybe there are some that are completely missing that I am unaware of. It seems like the oring on the upper thrust bearing race should keep oil from entering the top part of the column housing...but it is! There are three sets of plungers with springs in between them in the middle body, and one hole that I am guessing is a drain hole for oil to drain back into the gear box. Thehole looks decent sized, but it is just a tiny pinhole in the center. The I.D. Of the race is also larger than the steering shaft, so not sure what would keep oil from filling from there. This thing is frustrating me, and I have taken it apart more times than I care to mention. It really doesn't seem to be that complicated, but I am having a hard time with it anyway.