I had the same leak several years ago, slow and annoying, but not enough to cause panic. I ended up pulling the stern tube and rebedding it during a haulout. The process was not difficult but as I recall it took quite some time and effort to get the prop off, coupling off, shaft out, stuffing box off and stern tube out. It seems like might be possible to just pull the stern tube out a ways with the shaft still installed.
Kevin