Also, you must notice the Luzon is very far form West Coast. Distance affects effectiveness of TFs, maybe it has the same effect on convoys ? That being said, if you try to supply some closer base than Luzon, convoys are efficient.
Patrolling bases with a small single ship TF also has some effect, although pretty slow. At least I had some results with the Japanese. I've not checked yet for Allies.
As for the oil victory condition : Leyte has to be conquered before Japan is allowed to attack Borneo. Once you control Borneo, you have to repair the base and make it functionnal one full turn before the +1 oil bonus comes. But as long as Allies control Leyte (-1 oil), your -1 overall malus remains. You'll have to capture and repair Borneo or to capture Leyte before your oil supply rate switches to 0. But if my memories are right, if Allies re-capture Leyte, the -1 to bonus applies again even is Leyte is not repaired to be functionnal.
And now, my question.
The rules state that if a population center is bombed (Ceylan, Brisbane, etc.), then the owning player must patrol this center 1-4 month with at least 25% of his navy. Okay. But what happens if he does not patrol or doesn't use enough PV for patrolling ????