The corroded Y valve, minus another failed hose fitting, recently emerged from a heap o’ stuff on the Basement Laboratory Bench. This old photo gives you an idea of what happens to cheap pot metal in a garden:

I dropped it Y-end-down into a container of white vinegar for a week, after which a few minutes of scrubbing produced a workable result:

The threads on the left side are pretty much gone. The hose fitting protected the threads on the right, but was corroded firmly in place; a penetrating oil soak and concerted muttering removed it.
All of the garden hoses and fittings out in Mary’s Vassar Farms plot have survived well beyond their best-used-by date. Given that we salvaged many hoses from the Farm’s end-of-season midden heaps, they don’t owe us much …
The next iteration will have more brass …