Oliver, epenesa, ford. Phillips the year before, Dawkins the year before that. The Teller trade now looks like a mistake, as he's been a solid contributor for cleveland - demetrious johnson is a 7th round pick so i don't consider that much of an investment.
So... 6 total linemen in 4 years. Free agency is before the draft, but of the interior linemen i'm not sure they're set with butler, jefferson, phillips as the guys with oliver and star (who re-did his contract and will be returning in 2021). On offense the line is in flux - you have dawkins ford morse and younger depth players. Feliciano, Nsekhe, and Williams are all free agents.
You aren't getting stud linemen by trading for them so if you want to go from ok to good on the line, you need to invest draft capital. If they prioritize milano, I could see needs along the right side of the line.