what you are missing, is that with the redlne, because of its very high sheer loading, you can put the ultra light, (yellow) in it, wich is thinner than you motul gear300 and most of the other comonly used oils, but still has the mechanical protection of a thicker oil.
so the synchros can work better because of the lower viscosity. same a the old atf trick. just with more gear protection. we have fixed many zed boxes with the yellow.
yes its meant for a dogbox but does work. however if the detent springs and stuck to the magnet theres no oil that will fix it.