I got it fixed. Funny how it worked out. I took the cartridges out, and went into town to look for replacement packing seals, leaving Girlfriend at the cottage with no running water while I went treasure-hunting. Couldn't find any, but did find some O-rings that might have worked. I had some misgivings about using an O-ring for a packing seal because I thought it might be less durable than a proper packing seal over time, even with grease. (I also had a look at some graphite cord at a plumbing place, but all they had was a heavy gauge apparently meant for boilers.) Then on a hunch I stopped at one more place (Rona) to see if I could do better than the O-rings, and found an exact replacement kit for the the whole shebang! The package even indicated the dates (1950-68) for "Wallaceburg cartridge for Jubilee tub and shower" which evidently fits the old Jameco faucets, and this was a regular Master Plumber pack on sale in the regular section. I hesitated because I wasn't thrilled about paying three or four times more than the solution I had already figured out McGuivering the old fittings, but even more because I don't like the idea of buying and discarding perfectly good brass parts just because a seal had deteriorated. But I went ahead and replaced the entire cartridges and the faucets now work like new. It didn't occur to me until after I had them all installed that once I had tracked down the exact match for the cartridges, I could potentially have special ordered just the packing seals, but shutting off the water while I tinker with this isn't all that popular so it is best that the thing is fixed and done. Thanks for the tips along the way!