"unless it were" is correct and usable in written English.
You can use it when you want to express the idea of a condition or situation that is not the case. Example: I might take the job, unless it were too demanding.
Why change the water pump ("unless" it were changed recently): that's because the rubber seals of the old water pump get brittle and crack from engine heat and re-cooling -- and coolant washes out grease, so change it.
And unless it were really on its uppers, a nation that let its great public buildings run to seed would justly be accused of philistinism.
Even with the discount the government would get, it does not seem that it could acquire 10 million doses unless it were to spend some of its money on cheaper drugs like penicillin.
And if capital found it easier to come and go, the central bank would have to ease its grip on the exchange rate (unless it were willing to give up monetary control at home).
The company's chairman, Cesar Alierta, said offerings for its Data, Media and Emergia units would not go ahead "unless it were necessary to unlock value".
The SNP threatened to derail Brexit unless it were handed full control of the powers.
Britain, however, continues to oppose an FTT unless it were implemented worldwide.
withstanding a Turkish incursion, unless it were supported by U.S. airpower.
The Air Force wouldn't let Trump keep using his plane as president, though, unless it were significantly upgraded.
Unless it were linked to a full peace settlement, a withdrawal of U.S. and NATO forces would leave the Afghan government deeply vulnerable.
"I feel as if I could never be content with ordinary living again, unless it were to be broken by a return to the Arctic.
