Truis
You may have not mistreated your cameras. e.g. '90
I bought a 2nd hand OM-4 from a brick camera shop and they insisted I take a 1.8 away for free they offered a choice from five, 4x sleepy iris, one scratched so I took the highest serial number with perfect optics and expected to have to lens spanner it.
This was a late one with Japan on name plate which it turns out only needed three screws off to remove the lens mount face plate and all the lube on the aperature stop down mechanism removed, it will operate dry ok but gets sleepy even with traces of oil.
I have about four 1.8 now and the free choice is the best on a test chart beats the slight later final version, but only just.
But my suggestion was not made on this samply most OM for sale with any caveat have 'sleepy iris', dont know about e-bay, never look, GAS alert, oooh ahhhh ooooh aaah.
We can ask the forums ex-OM spanner person how many 1.8s he estimated for, the 1.8s were so cheap new it was simpler to discard as junk.
Noel