Position C is absolutely right. If you want to call Position A above the 2 flanges that hold the circular spin plate ("disc") in place, and Position B between the 2 flanges I found 4 thin washers in Position C, which I left in place and put a set of 4 new washers on top these (between the base and the two sets of flanges on either side.) The result is that you bringing the disc up slightly higher to make up for the worn-down nylon ring. Final result - no wobble.
If you want to avoid disassembling the whole seat mechanism (as per Mystery Machines' mod instructions) then I don't see that it makes a difference if the new washers are above or below your existing washers, just make sure they are in Position C. Yesterday I put them in position B and just made the wobble worse. If you have washers in there take them out. I also had washers under the disk, which I removed. Washers in Position A make no difference one way or the other, except that the bolts need a washer and a lock washer, obviously.
New no-struggle reassembly process:
While reassembling I discovered the following order to be easier, and eliminates having to wrestle the whole damn seat into place at the end:
1. Re-torque the four 6mm hex head bolts going through the 2 flanges that hold the disc.
2. Place the seat bottom upside down on a milk crate or something (to keep it clean). Place the metal base (upside down) on top of the 4 bolts coming up off the seat bottom.
3. Find the 2 nylon cuffs that go onto the 2 release links on the base and replace them (you did take them off and put them somewhere safe, didn't you?) Attach the 2 levers from the seat to the 2 release links on the base and replace the R-clips. I used a set of vice grips to hold things together while I put in the R-clips. Pull the seat belt through the loop in the seat to get it out of the way.
4. Now replace and torque the four 12 mm nuts that hold the seat base to the seat.
5. Flip over the seat+base and go install it to the runners on the Delica with the the four 14mm lock washers and nuts. I found this challenging until I realized I had bent the tabs that go into the track between the bolts as I was removing the heavy, heavy seat. (I bent them back to right angles with an adjustable wrench - no problem). Once installed the seat+base is happy to rotate through 360 degrees, presenting you with the side you're working on at eye level while you squat outside the Delica's sliding door. No more heavy lifting! Rotate the seat so the rear is facing you.
6. Lay the seat back onto the seat, replace the extended-head 10 mm hex bolt, lock nut and washer combo on the right side of the seat back, then the two 14 mm hex bolts on the left side of the seat back.
7. Rotate the seat round while you reinstall the left and right plastic trim panels. Careful - the rear screw on the left panel is a different size than all the rest of the trim screws. Replace the handles of the 3 release levers on the left side.
8. Reinstall the front and back plastic trim panels. Clip them into the top of the left and right panels first, then push them down and snap the 4 pins into the holes of the other 2 panels. You might need to push the left and right panels together to get everything to clip into place. Now install the 2 trim screw into the front and the back panels.
9. Sit on your captains chair and rock back and forth. If the wobble is gone then great. Otherwise you have to go through the whole process again and add another set of washers where you put the first four. It gets much faster the second and third time you do this.
