Orcs... were elves?

[Boromir88]

Only Orks with pureblooded Elven ancestry (tormented by Morgoth or no) would be immortal.~Formendacil

But the question is were there ever any "pure-blooded" through and through Elf corrupted into an Orc. We are told this from Home X, but it goes along with the "Man Origin."

They could be slain, and they were subject to disease; but apart from these ills they were not immortal, even according to the manner of the Quendi; indeed they appear to have been by nature short-lived compared with the span of Men of higher race, such as the Edain

Again this applies more directly to the Mannish Origin, but it is (as far as I know) the only quote that talks about Orc life-span. Also notice that even the Elves believe Orcs were not immortal.