This is the problem with perforated leather. You will always get dirt into the pores, it is a physical impossibly to keep it 100% clean. No matter what cleaning agent you use, some will always travel INTO the holes

Vacuum as much as you can, soft brush to loosen it up, revac... then pick any leather cleaner, use water and judgment to figure out how best to flush the debris. I use lexol on all my leather seats.