Some solid OL have had slow starts and changed teams and gone on to long careers.
This is the first guy that came to mind. Image: http://t3.gstatic.com/images?q=tbn:ANd9GcRkKCsHhxfVOAP9MqxX0ajNC2yHG1E2P8aYxUxScJ3NyOQrP4-h
Tony Mandarich was the second overall pick in 1989, was cut in 1992 and is considered one of the NFL biggest busts.
However, after some time out of football, he came back and was a starter between 1996 and 1998 with the Indianapolis Colts.
Even though I think he's a little overrated, Andre Smith from the Bengals.
Through two-plus seasons after being taken No. 6 overall in the 2009 draft, Andre Smith looked like he might be a massive bust. Then, rather suddenly, the light came on — Smith closed the 2011 season with several solid performances, then in 2012 played as one of the NFL’s elite right tackles.
Andre Davis was selected second overall in the 2001 NFL Draft by the Arizona Cardinals, and played guard his first three years in the NFL and was on the fast track to being a bust. The Cardinals didn't resign him and he went to Dallas where he became a pro bowler.
Chris Williams was drafted by the Bears 14th overall in the 2008 NFL Draft. Had injury problems and probably hasn't lived up to his potential, but is becoming a steady starter.