Since we're allready in NEPRT and I've been watching this thread let me add that buying some of these lubricants is really all about marketing. Yamaha is not in the lubricant business. Neither is Wal-Mart.
They both accept bids from lubricant companies that meet a certain spec. (There is nothing inherently unique about a Yamaha final drive. If the engineers call for a GL-5 lubricant for the drive, any GL-5 lubricant will be acceptable.)
Their branded lubricants are then blended and packaged by whoever the low bidder is for that contract. The duration may be for X-years, it may be for X-gallons.
So that jug of "special Yamaha lube" may in fact be poured from the exact same spigot that the jug of Quaker State lube at AutoZone was filled from. Or it may be Valvoline, Pennzoil, Shell, Mobil, etc.
In fact if the bid is awarded to another company at the end of a contract, it's not impossible that two bottles of Yamaha lube sitting on a dealers shelf (one older, one newer) could be from two different lubricant companies.