If you use your Leatherman regularly, there is no need to any oiling, as that will create an unneeded mess, and dust or sand mixed with oil will only abrade parts of your priced tool.
More important is to keep it clean and dry. If it gets severly soiled, wash it with soap and water, wipe well and let it dry with the tools open and out of the pouch. Remember it is made of stainless and well resistant to rust and corrossion (unles you bath it in sea water and leave it to rot in the pouch- OUCH!! OOPS)