Much earlier, someone wrote (and I'm sorry I didn't clip who did so):
<< Originally "Ol' 97" said, "It was on that grade that he lost his average," meaning average air pressure in the brake lines. Very, very few people would understand that, so I have no prob staying with "lost his air brakes," even though that isn't original. >>
Actually, the original WAS "air brakes," but the popular version, sung by Vernon Dalhart, who had to learn it from the recording by the original singer*, changed it to "average." So the "change" to "air brakes" is actually reverting to the original.
Of course, music transcribers have a lot to answer for, especially when the artist doesn't care to check the printed lyrics (the opposite of Ralph McTell's problem). To wit, Dylan's words in the songbooks produced by his publisher include "The highway is for gamblers, better use your sins..." when he's clearly saying (somewhat nasally) "... use your sense."
I tend to try to keep to the traditional "sins" when I sing, but often go back to sources instead of parroting the garbled version a trad singer may have come up with. I sing "Wildwood Flower" without the "pale and the leader and the eyes look like blue." And I've been known to sing a song as written even when the PC thing would be to change it ("She was Mex and I was white," from "Border Affair," for example), though I'm careful with audience sensitivities when I do this.
I've even changed songs written by contemporary writers, such as changing "Put to music and sing to you" (in Old Bill Pickett) to "Learn the music and sing to you," since I'm not the one who put to music the lines old Zack Miller wrote (look up the lyric if this is cryptic).
And sometimes mondegreens are hard to get out of your head, even when you don't want to sing 'em that way. From "Hello, Stranger:"
Get up rounder / Than you were when you lay down ... is HARD to keep from singing, even when I know it's wrong!
* Anyone remember who that was? My mind is mush today (and why is this day any different, you ask?).