I changed the gear oil in my F150 last month. I noticed that there was a green/blue color oil that came out but the new Yamalube I put in wasn't the same thing. I checked the container again and it says for use in all Yamaha outboards.
Whats got me thinking is I read somewhere that the consensus was that Mercury premium was the best gear lube to use and that a lot of Yamaha tech's use and recommend that product. I just want to use the best product available for my motor. I'm wondering if I should change to Mercury Premium now, instead of waiting until the next scheduled service? If what came out of it was synthetic and I've changed to dyno, I need to change back to synthetic, now and not wait, right, or not?

The blue colored oil you drained was a different brand as Yamaha uses a lube similar to an amber colored 90 hypoid. There is no reason to switch brands at the moment as the Yamaha oil is what is recomended for your motor and you are not abusing the F150 by racing or commercial use.

One of the boating magazines is conducting lower unit oil testing and says they will publish the results in a couple of months. It should be interesting and informative. They would not give out any more info than that.

Thanks Doc,
You answered my question quit nicely.
G'Day