I found this undated article from Time Magazine during WWII about Senator Harry Truman holding hearings on the safety of Liberty ships. He is basically informed that about 3.2% of the ships are defective, just like any other type of new ships.http://www.time.com/time/magazine/article/0,9171,791438,00.html

The former master of the Liberty ship, Henry Ward Beecher, will tell Truman that he had logged 61,000 miles on that ship without any trouble, including sailing in the cold waters south of Australia. In fact the Beecher's maiden voyage out of Los Angeles took her to Wellington, NZ, then on to Bombay, India, to Karachi (present day Pakistan), then down the west coast of Africa to Capetown, where she will sail in her first convoy for a few days to get away from the coast, then to Bahia, Brazil, then on in coastal convoys to the US,

I got on the Beecher in November 1944, when she must have been approaching the 90,000 mile mark, and made two extensive cruises on her, with only rudder trouble on one occasion off the Virginia coast during a bad storm. But on a previous occasion I was on a fairly new Liberty ship that was scratched from a Russian convoy at Loch Ewe because of boiler problems.

We must remember that merchant ships and crews generally did not go on "shake-down" cruises the way navy ships did, nor come into port for an occasional refit. The first voyage of a Liberty ship was also its shake-down test, and hopefully it would not straggle.