Why Michigan's facing another offensive line rebuild, and the outlook for 2017

ANN ARBOR -- The song remains the same.

For Led Zeppelin's Robert Plant and Jimmy Page, this sentence represented a nearly 6-minute instrumental with lyrics focused on dreams and global travel.

For Jim Harbaugh and Tim Drevno, it represents Michigan's seemingly endless quest to rebuild an offensive line that cannot seem to get itself over the hump and continues to be the biggest obstacle between the Wolverines and a championship.

Drevno -- Michigan's offensive line coach/offensive coordinator -- has done this before, of course. He helped Harbaugh build one of the country's most feared power rushing attacks at Stanford in the late 2000s and had to re-tool a USC line in 2014 that featured three…