Update: I opted to do nothing about the leak. I changed oil in early Spring, and have driven it about the same as last season -- about 5,000 miles per year, mostly pulling a single-axle trailer filled with mowers and equipment.
I still get a very small leak, small spots on the driveway where it is parked, but only periodically. I changed oil in mid-Summer as well. Between the Spring change, and the Summer change, I added one quart to top it off. Since the mid-Summer change, I have added one quart. So, I am loosing about a quart every 2,500 miles, over a three month period. The leak does not appear to be progressing.
I now believe I made the right decision to do nothing. I'm more than happy to add one quart of oil now and then, rather than having spent $3,000 on the repair. Actually, I am happy to add the one quart, knowing I didn't spend $3,000. A couple of quarts of oil is very cheap, over against the repair.