One of the great drawbacks of urethane bushings is the fact that the bushings eventually dry out, start to stick, squeak and eventually destroy themselves. This isn't water washing the grease out, it's the bushing wiping the bearing clean and squeezing the grease out the ends. After only about 800 street miles and none in rain, I started to see my original Powerflex bushings drying out (when I was replacing them with SuperPros, which are internally knurled, but that's a different story)
In searching, I found a vendor on the Miata forums that sells a sleeve bearing retrofit for urethane bushings for those cars. This converts the single crush bearing to an inner stationary bearing and two outer sleeves (that are oil impregnated but I'll grease them). The idea is that the bushing doesn't rotate on the bearing anymore. The outer sleeve and bushing rotate (as one unit) around the inner stationary bearing.
He's been making them for Miatas for 3+ years and has been getting great reviews so I asked if he could make some for the Elise. Here's the description that I found online.
Using the Superpro bushings, which have a larger crush washer diameter than Powerflex, he made me a set.
On Miatas, they have room for a zerk fitting to regrease the bearing periodically. We don't have space for a zerk in a couple of locations so I decided to just leave the zerk off and see how long these last with the grease from the initial installation.
I'm not sure when I'll get to installing these on my car, but will report back when I do. Here's a picture of the set for my Elise.