I don't think there's anything to lube. Every time I wash ours and wipe down the door jambs, I press the rag against the bottom roller and slide the door slowly. Living in FL, there's a lot of sand, duh! But the rollers have bearings, so they should be sealed. The rear rollers (where the latch is located) slide in a track that appears to have some lithium grease, but besides cleaning the rollers and tracks, I wouldn't go crazy with grease.
Edit: I've looked through the service manual at the information about the doors, and find no reference or symbol that grease or oil is req'd.