Did you polish the crank while you had the old seal out?
I'm not an engine man, but our local engine shops occasionally have a leaky crank seal. They remove the old seal, then disconnect the plug leads, pull all top sparkplugs. Then one person using a piece of very fine emery cloth, or micromesh, will hold it onto the area of the crank where the seal contacts, while another cranks the engine.
Some specialty shops also cadium plate the crank flange (all the area of the crank that is not exposed to engine oil), for protection from the elements. Sometimes this plating just happens to stop at this location where the seal rides. You can still fix it with the above procedure

We had the same sort of issue come up on our Club Archer with an O-360. Turned out to be a case halfs were dribbling a bit. This case was one of an engine at TBO and was to be majored soon so it was band aided for a month until major. Might be worth checking though.

my 2 cents

Vin

Dave,
You can try some sealant on the seam and it might help for a short while.  Other than that, splitting the case halves is the only way to fix it.  If it's not leaking a LOT (i.e. a qt. every 4 hours), I would fly it--many engines over 1000 hrs develop case half weeping.  Is it leaking around the cyl through-bolts by any chance?

My engine quit leaking at the crank seal. Oddest thing...I put approx 7 hrs on it after the seal was changed (those hrs also put me due for an oil change) and it still would seep at the new seal. I changed my oil and filter, replentished the engine with Aeroshell 15/50 and took it for a 30-45 min flight, and found that it still had seeped (I always cleaned off the oil after every flight).
I had been planning on flying to Sun-n-fun and was not going to let a little leak stop me. I put 7.5 hrs on the tack (stopping once for fuel) flying to sunny FLA and when I got there there wasn't a trace of oil. I have since put on about 25 hrs and it hasn't leaked a drop. Matter of fact, the oil level has only dropped about 3/4 of a quart on the dipstick in the 32 hrs since the oil change.

I have had a problem with my Mooney M20J IO360. I have now gone through three crankshaft seals (the original, and two new replacements). They have started to leak. My mechanic glued (what glue is best?) the last one in place, but it didn't help. He thinks it is because I fly a fast airplane and fly fast up to the airport and then cut power too quickly. I usually fly full-power for a 1/2 hour commute, and for the last 8 miles lose 3500 feet by first setting manifold pressure to 16" and then nosing down at 180 knotts for a 1000 to 1500 foot descent. When I get to traffic pattern altitude 2 miles away, I level out for a mile which brings me slow enough to put the landing gear down and also full flaps shortly afterwards. I am then 1 mile from the airport at 80 knotts IAS. I cut power virtually all the way and slip down for the landing.

Is the sudden decrease from 24" manifold pressure to 16 causing the crankshaft seal to have blow-by and then start leaking? Or is it the setting from 16" to idle on the final descent?

The articles I have read so far don't deal with this specifically.  Any thoughts?

Thanks,

Jim