Slotted.
From "America's Hundred Thousand" by Francis Dean, p47 structural description:
"The landing flaps, representing 13 percent of the total projected wing area, were NACA slotted type. They were hydraulically operated, and during extension moved first aft and then down, and during retraction moved first up then forward. The movement ws synchronized by three trapezoidal linkage hinges to ensure accurate positioning of the flap agianst the main wing panel to maintain the proper airfoil. The links were synchronized by attachment to a torque tube, and the assembly was attached to the inboard auxiliary wing spar. Independent units either side were synchronized by the hydraulic system. The flap linkage assembly was bolted to the flaps. The double-cambered extermal surfaces of the flaps were formed by flanged nose and tail ribs attached to a single spar. Additional light nose ribs were provided between basic rib locations."
Hope it helps.