Attached is the parts diagram, which may help the conversation. Frank, did you make a part that fits between parts #14? In the original design did tightening the nut/bolt draw the two #14 pieces together thereby compressing the #13 rubber bushing, causing it to expand and lock against the sleeve of part #12? Did a metal spacer between parts #14 would allow tightening of the nut/bolt without squeezing the #13 rubber bushing?
As an alternate approach, I replaced my worn rubber bushing with polyurethane. More info here-
http://www.lotuseuropa.org/LotusForum/index.php?topic=62.0 Also, follow that link for info on how I got fifth gear to work.
To achieve shifting nirvana I believe you need to address the bushings (#3) at the bottom of the shift lever(#2), the center link/middle pivot (#11, 12, 13, & 14), the rear linkage attachment at the gearbox (right/back end of #10), AND have the length of the linkage properly adjusted (adjustment done where #9 threads to 8 & 10). If any of the plastic or rubber bushings are sloppy, the shifting will be sloppy. If the linkage attachment at the gearbox is loose, you will have shifting problems. If any part of the center pivot is loose, you will have shifting problems. If everything is tight but out of adjustment at the center pivot or the gearbox, you will have shifting problems. But when all is right, it does work.
I haven't quite reached nirvana but can find all 5 gears and reverse all the time without feeling like I'm stirring pudding. Everything works! My only annoyance is a rattling noise from the bottom of the shift lever. I am using oilite bushings (with an original type shoulder bolt from RD) and wonder if the original design plastic bushing would cure the rattling noise, but at the cost of decreased durability. I have plastic bushings from RD but the rattle is not enough motivation to reach back into the tunnel to install them!