Fall 2016, returned from a trip, went to change the oil.
The filter (Fram CH6012) comes with a big and a little O-ring. The little O-ring was fine and went happily onto the bolt and into the flange.
Unfortunately, the big O-ring was folded up like a pretzel. I assumed the big O-ring would hold a round shape, once it was stuffed into the flange groove. Unfortunately, during assembly, the big O-ring sneaked out of the groove and was compressed under the flange. Oil flowed out freely. This is onto the garage floor of the condo I had just moved into, where you're not 'supposed' to do engine work in the parking space.
Drained the oil, replaced the new big O-ring with the old one, reassembled, refilled. Perhaps as I was flustered from cursing the pretzel O-ring, I didn't tighten to the 14.5 ft-lb torque I was supposed to. Put the bike away for the winter.
Come spring, I noticed leaking, went through the diagnostic bit, and eventually tightened the damn filter bolt. Now all is well.
Oh, well, it's a hobby.