I know this sounds remedial, but make sure your oiler gear tang is actually engaging the sprocket groove, and is being pulled as the sprocket rotates.
Sometimes the tang looks fine, but if it wears enough, the outer tip will break off clean.
The way I verify oil output on saws before I start them, Is to spin a Dremel 502 or 503 flap wheel against the outside of the sprocket drum, and spin the sprocket up by until it starts weeping out the output hole, ( with the bar off ) obviously......
Another thing worth mentioning is that sometimes I've seen bars on saws that people have used a grinder or drill on to make them "fit" a saw, and the oiler hole doesn't always line up.