1. Michael Onwenu
Onwenu has been moved around the offensive line regularly by the Patriots over his first four seasons, playing every spot but center. He settled back at right tackle for the final 11 games last season, and played very well (three sacks allowed). That versatility will serve him very well on the free agent market, and teams could see him as a tackle or a guard.
The Lions would definitely place high value on Onwenu's versatility. But Penei Sewell is not going anywhere at right tackle for the foreseeable future, so they'd likely see him as the prospective starter at right guard first and foremost. A right side of the Lions line featuring Onwenu and Sewell for the next, say, 4-5 years (at least)? That sound you just heard is opposing defenses shaking in their boots at the mere mention of the idea.
Onwenu (6-foot-3, 350 pounds) is simply a people-mover in the run game, using his size, strength and footwork to overcome not being, as Pro Football Focus felt the need to say for some reason, "the quickest player off the line." As big as he is not being the "quickest" off the line feels expected, and it should not be framed as a knock on him.
If Glasgow finds a noticeably better contract elsewhere, which it feels like it'd have to be for him to leave the Lions, he should take it. Among the pivot options to replace him, Onwenu (26 years old) stands atop the heap, even as he will certainly have plenty of suitors. As a Detroit native and a Michigan alum, maybe he'd like to return home if offers are equal.