There’s a revolving door of lefties in the Boston Red Sox bullpen. Will it continue to turn with the trade deadline approaching?

The Red Sox have already used 23 different pitchers this season. That’s the most in the majors, and just two fewer than they used all last season. It’s mostly due to the lack of a consistent left-handed reliever.

The offseason revamp of the bullpen brought in several established relievers, all right-handed. A southpaw was supposed to emerge from the hodgepodge of retreads and fringe candidates assembled by the front office.

The job started with Dennys Reyes, but he managed to retire just four of the 10 batters he faced. Since that initial plan failed, the Red Sox have continued to throw lefties against the wall, hoping one might stick.

Hideki Okajima blew a shot to reclaim his old role, while Felix Doubront and Tommy Hottovy both came and went. Rich Hill was brilliant in his brief stint. Lefties finished 1-for-14 (.071) against him before a torn ligament ended his season.

The lefty reliever with the most days on Boston’s 25-man roster? Franklin Morales.

Throw in Randy Williams, the latest lefty to audition, and seven left-handed pitchers have pitched out of the Red Sox bullpen this season. That doesn’t include Andrew Miller or Jon Lester, both of whom have exclusively started games. Only twice before have the Red Sox used nine southpaw pitchers in a season (2004, 2005). Another lefty will mean a franchise record.

With the trade deadline approaching, that 10th lefty is the most obvious hole for the Red Sox to fill.

Jim Bowden’s Big Board provides insight into just who might be available to fill that role. Sean Marshall tops the list, and with a 3.04 ERA would be a worthy addition to any bullpen regardless of which arm he uses the throw. At just 28 and under contract for another season, Marshall’s cost likely exceeds Boston’s need.

The Red Sox bullpen is already overflowing with quality relief options. Matt Albers has allowed one run in his last 20 1/3 innings. Despite a 1.99 ERA since returning from the disabled list, Dan Wheeler has been relegated to mop-up duty. And that doesn’t even include any future contributions from Bobby Jenks.

Indeed, any need for a lefty is purely for situational purposes.

With a long track record of success, Brian Fuentes might seem like an option. However, just because he throws lefty doesn’t mean he gets them out (.315 Opp BA vs LHH).

That leaves the Marlins’ Randy Choate as the elite available lefty specialist. He’s held lefties to a .121 batting average this season (7-for-58), the second lowest in the majors among left-handed pitchers (min. 50 batters faced).

Only Javier Lopez (.108) has been tougher against lefties. That the Red Sox gave him away at last year’s deadline shows just how unpredictable these pitchers can be.

Florida’s Mike Dunn is fourth on Bowden’s list. He’s held lefties to a .171 BA, but 13 walks have led to a .306 OBP.

The market for a true lefty specialist appears thin. That leads to the question: Do the Red Sox really need a lefty in the bullpen?

The key cogs in Boston’s bullpen may all be right-handed, but each has had significant success against lefties.

Jonathan Papelbon (.198 Opp BA), Alfredo Aceves (.200), Albers (.207) and Daniel Bard (.211) have all held lefties to low averages. As a group, Red Sox right-handed relievers have held lefties to a .238 BA and .684 OPS. That’s allowed Boston to go without a dominant lefty all season.

In other words, the current roster can hold the fort.

The question comes in the postseason, when one at-bat could determine the season. With Curtis Granderson or Ryan Howard stepping to the plate in the seventh inning, there’s no logical option that instills confidence.

Who can the Red Sox trust to get that one out?

Well, Choate hasn’t been able to solve Granderson, who is 5-for-6 lifetime against him.

But he might just be the perfect option for a potential World Series matchup with the Philadelphia Phillies.

Howard and Chase Utley are a combined 1-for-14 against Choate.