Every year (during the car washing time of year) we get into several water softener device discussions -- often that folks were disappointed with the lifespan of the small units built into nozzles -- they don't last long, and they don't soften enough.. The last time, last summer, I mentioned that I had seen a water softener using a large cartridge, but I couldn't remember where I saw it.
Well, I saw it again in a catalog, Griot's, and ordered one -- it's catalog # 37244. That cartridge is huge, bigger than it looks in the picture in the catalog, a cylinder 4 inches wide and over a foot long -- this should last a few washings!
I haven't tried it yet -- it's not yet wash-your-car-by-hand temperatures yet here, but it looks promising so far. I'll report back again after I do my first hand wash (when I uncover and wash my '93; I've been using my '84 during the winter salt season).
Meanwhile, I took a picture of the complete kit, but the "gallery" part of this website isn't working right now, so I'll post it later.

Regards to all.