Seafoam works well, but i've always been told not to mix it with your oil if your motor has alot of miles on it. Its just personal opinion....but I dont see the benefits of running it through the motor over risking creating an oil leak somewhere because it ate through one of the seals.
I know he has a manual....I know the kid personally. Im just saying i've never heard of someone putting 10w-30 in a transmission (auto or manual)
aisin recommended 10w30 for the manual transmission equivalent of the AX-15 in the toyota trucks.
that said. Redline GL3 MT90 is the best thing I ever did for my trans.