Following a night of practicing approaches, I dutifully put the plane back in the hangar. The next morning I went back out to the hangar to replace the EGT4 sensor which had stopped functioning. When I looked at the plane, I saw that my engine seemed to have burped oil overnight. Based on the oil drip paths, it seems not to have happened in flight or even on the ground during taxi. At this point, the aircraft had 411 hours.
Viewing the aft side of the ring gear found oil of course, but also some kind of flexible material that I later determined was some cured sealant holding the crankcase in, perhaps showing the source of the failure.
Now it was time to learn how to remove and replace the crankshaft seal. Lycoming has a service instruction for that (1324D). Removal of my crankshaft seal (which of course requires removal of the propeller), showed sealant missing in the grooves, though that sealant may have detached during removal.
Installation of the replacement seal requires a special tool. Lycoming has one for more nearly $2k. ATS has one for just over $100, so I went the latter option. I didn't capture images when I was using the tool since it requires two hands and I was working solo. I did grab a snap when the seal was in place and also when I was pushing the spring in with a bike tube replacement tool (prior to application of Dow Corning 737). It also made sense to replace the alternator belt (a Dayco 15355), though the original one had no signs of wear on it that I could see.
Following reinstall of the prop and a ground test, the new crankshaft seal has been functioning properly. So that was an interesting experience.
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