Here's what I did in my shop (20 Mins.).
Cost: Zip, zero, nada.
Caveat: Lever not removable on Evos (5spd) unless primary pulled.
Twin cams are different.

Re.: 1996 FLHTCI, 1st Yr. injected.

1. Removed allan bolt.
2. Used cutting wheel on Dremel w/flexible extension.
3. Guided wheel into existing pinch gap on existing lever. Used variable speed to carefully glide wheel back and forth, also, fingers to reposition lever on shaft as needed, to clean out, widen pinch gap nearest the shaft.
4. Squirted with brake cleaner.
5. Hit with air hose.
6. Used same allan bolt.
7. As I tightened bolt, could feel lever compressing, getting a new "pinch".
8. Actually tightened bolt to less than previous unsuccessful whammy torque.
9. Lever is tight--very tight on shaft now.
10. Will replace allan with Grade 8 Hex (5/16 24 x 1???)

Note: There is actually adequate room between the primary and trans to do this. Did not even have to put bike on lift.

Prognosis: Let's see if I can get another 35K miles on it.

Prequel: How I came to this plan.
If bolt is whammy tight onto lever, and if lever not compressing onto shaft, and lever is still floating around loosely on shaft, then, obstruction in pinch gap. Possibly bad original design or manufacture results in pinch gap closing on itself, nearest the shaft. Have seen some of these old bad levers, and it looks that way to me. The pinch gap does not remain parallel, instead, it meets itself at the inner end, closest to the shaft,
while the outer end, farthermost from the shaft is still showing a gap.
Thus, remove material from the pinch gap, closest to the shaft, and the lever should be able to tighten onto the shaft.

Please, hold your applause for the next 35K miles.

ADDENDUM: NECaveman has a good point Re. a shank bolt.

HD uses the wrong bolt, a fully threaded allan, 1 inch 5/16/24.
Should use a shank bolt. Threaded bolt eventually looses its threads at the shaft groove,
and will drift out the entire length of shaft. This should not happen even if bolt is loose.
Could not find appropriate shank bolt at Ace hardware, but found a workaround on a 1 1/2 stainless.
Shank is the right length, cut bolt down to size, cleaned up the threads, works perfectly.

Photos.

 

This lever actually fell off my 2009 SG on a ride last year. Two issues. (1) The pinch gap needs to be increased like Panco25 explained. (2) HD specifies the incorrect type bolt with threads cut up to the bolt head. Find a bolt that fits that has a shank, without threads, that contacts the trans shaft. The HD bolt has about a 1/16 inch contact point of two thread portions on the trans shaft. After a period of vibration the threads wear and like on my bike the shift lever vibrates off the trans shaft with the bolt torqued into the lever. I used another HD bolt on my 2009 SG and will source a proper replacement bolt next week when I pick up my 2014 RK.

 

Nicely done.
Looking forward to the bolt info.

 

Took you advice on the shank bolt, and amended original post.
Thanks.