lubrication 2001 F25 4 stroke

[blgrdiablo]

During a 4 day trip to the calofornia Delta, running 4 to 5 hours a day at various speeds I noticed that the 10W30 Yamalube I am using broke down a bit. I want to switch to 10W40 but Yamalube does not make it. What is a good 10W40 oil I could switch to? I have easy access to the West Marine Brand, it is marketed as premioum semi-synthetic.
Thanks for your input.