So, back on topic. All you warranty-worry-worts, who think Yamaha would decline a claim because the exact perfect formulation they think should be in there isn't in there, please explain this:...
It'd never be a problem for anyone unless they happen to be that 1 in 10,000 that actually had a final drive problem during the warranty or YES. Then, perhaps even more so because it is so rare of an event, they would naturally want to try and find out what was different about yours that resulted in your rare problem.
They would ask you for proof that you had the unit serviced per the maintenance schedule, and if you are a DIY guy that means you'll need receipts (not just annotations in a log book that can easily be fabricated) for stuff like the filters and oil. That is how they would see what you've been using in your engine or final drive, not through some sort of exotic oil analysis.
I think the fact that they have previously published the GL5 spec, and also some various oil weights per ambient temp charts in some prior years that have the identical final drives and engines installed is all you would need to be able to say that the lube or oil that you've been using is appropriate. So that is a non-issue.
I've already said that I am not worried about it myself. I already have Mobil 1 in both the engine cases and the final drive of my new bike during the warranty. But what of those ignorant FJR owners that do not happen to participate in this forum, and therefore do not know about those alternate specs in the other model years, etc. They are going to think that the Yamaha proprietary stuff
has to be used in the FD. It's a pretty shady marketing ploy for Yamaha to have used, IMO. I love their motorcycle product(s)... I don't love when they publish proprietary specifications like that.