Several texts of the song in Cohen and in the Frank C Brown Collection of North Carolina Folklore have the word "average" replacing "airbrakes". "average" can be traced to a recording of Vernon Dalhart's. He misunderstod the word "airbrakes" on an earlier recording by Henry Whitter. Dalhart was also apparently responsible for changing "Spencer" to "Center" and "Steve" to "Pete" and "begin to scream" to "broke into a scream". Those phrases are indicative of versions that descended from Dalhart's record. "leverage" likely arose because someone thought "average" didn't make sense tried to rationalize a different word "leverage". Unfortuantely leverage makes no more sense than average, since leverage is the force applied by a lever to lift or pry an object. If he had lost his ability to pry himself off the track he would have stayed on the track. Norm Cazden has an extended discussion of how folk singers often rationalize a sound alike word because they do not know what the original was. Cazden's discussion is in the context of the lumber camp song "Jack Haggarty" (which is the subject of another thread that I amuse myself with from time to time) but has broader applications.

Among the FCBCNCF's 6 texts is one that includes as a chorus:

Did she ever pull in? No, she never pulled in,
Though at one forty-five she was due.
For hours and hours has the switchman been watching
For the mail train that never came through.

There's nothing here about never "returning" and it makes at least a plausible chorus for a railroad situation.

rich r