Do you have a after market pinion support, Like a MW? I had a similar problem and had to RTV the spline on the pinion, where it slides into the yoke. The lube was actually coming through the spline and yoke. I had a leak and chased it for a while, and had to do it on two different center sections, both have after market pinion support/bearing
And I would pull the third member to fix the leak. You might be able to get away with just pulling the pinion support, depends on how lucky you are.