I'm adding this post for anyone interested or anyone who has run into
the same problem. I've implemented a fix that has worked for me.
After removing the e-ring, I drilled out the threads of a 1/4" T-nut
using a 1/4" drill, then slipped the T-nut over the threaded shaft.
With the shaft correctly mounted in the base and the flange of the
T-nut against the flange that the e-ring rested against, scratch a
mark around the shaft where the other end of the T-nut sleeve meets
the shaft.
Now remove the shaft and the T-nut from the base.
Using my drill with a diamond cutting wheel (a few bucks for the wheel
from Harbor Freight), cut a groove around the shaft. Let the groove
extend from about 1/16" above the scratch mark to about 1/16" below
it. Cut the depth of the groove so that the final diameter of the
groove is about half the diameter of the shaft.
Using some abrasive, such as sandpaper, abrade the surface of the
shaft to roughen it.
Clean the shaft and the T-nut with acetone to remove all oils and
grease.
Assemble the shaft and T-nut back onto the base. When the shaft and
T-nut are seated properly, the sleeve of the T-nut should extend about
half-way across the width of the new groove. The other half of the
groove should be exposed.
Mix a two-part, 5-minute epoxy. Glop the epoxy onto the end of the
T-nut sleeve and into the groove on the shaft, being sure to get epoxy
completely into the groove, up under the end of the T-nut sleeve. Be
generous with the epoxy. Spread it thickly, including over the end of
the T-nut sleeve and on the shaft beyond the groove.
Patiently watch the assembly after the epoxy has been applied. Prevent
the epoxy from forming a drip on one side or wetting down the inside
of the T-nut sleeve. You don't want to epoxy the T-nut to the router
base, only the threaded shaft. If you've used 5-minute epoxy, it
should stiffen fairly quickly. Once that happens, allow at least 24
hours for the epoxy to cure.
The threaded shaft should now be held securely in the fixed base and
the router lift feature should work reliably.