For 25 years, Dick Pleasants hosted the Folk Heritage show on WGBH-FM, playing countless songs from up-and-coming folkies. For the past 15 years he’s been behind the mic on WUMB-FM in Boston. And tonight (Jan. 7) he’ll be the guest of honor at “A Pleasant(s) Evening at Sanders Theater: A Tribute to Dick Pleasants from his Friends.” Folk music icon Tom Rush told the Patriot Ledger in Quincy, Mass., that Pleasants is “one of the heroes who have championed this music for decades. He’s been enormously important playing the new stuff as it has come along and keeping the old stuff out there in people’s ears.” A dozen performers will pay tribute at this evening’s show, which is sold out. Pleasants has been coping with Parkinson’s disease and will have a knee replacement next month — but he’s still at his weekend WUMB gig.