Update:
Turns out my Spanish skills let me down, and it was really a Bradley
tub faucet, not a kitchen faucet.
It also turned out that most of the shower tiles were missing, the drywall beneath them was all rotted out, and there was black mold everywhere. Water was spraying out of the faucet into the tub, behind the tub...
The plumbing supply house said they could special order a cartridge, but I decided to try the Danco "perfect match," instead, from the hardware store. It looked just like the one I pulled out, and all the seals were the same. But, after I installed the kit, water was still dripping out of the faucet. The owner said he had been using the Danco for years, and it always worked until recently. I figure there must be some defect in the valve body itself. I told him to call a plumber to replace the whole thing with a Delta, and I would come back to retile his shower. He said, he thinks his homeowners insurance will pay for everything. I said, "Good luck with that," and I got the hell out of there.
BTW, in addition to the moldy, rotted hell-hole of a bathroom, all the doors were kicked in and all the wall plate covers were missing, exposing hot wires to their children. Incredibly, they had a giant flat screen TV and a brand new F-150 truck parked in the driveway.