Eschew WD-40 unless you want the rails coated with a thick waxy deposit that will require disassembly to remove. I'd try one of the "dry lubes" for bicycle chains, your dry MoS2 lube might be good also. You don't want anything to attract dust, or anything that will thicken.
If the bellows are leather, use Lexol or Neatsfoot oil. If they're not leather, leave them alone.