After much troubleshooting, I narrowed the leak down to either the filter head or the water supply line. So I changed them both. Changing them was fairly easy, about an hour job for each, not counting testing. No special tools or special setups required.
The refrigerator manual is not clear about removing/replacing the water filter. In spite of what it says, the top shelf under the filter MUST be removed when changing the water filter. If you don't pull the filter all the way down, you may damage the filter assembly head. So remove the top shelf when you change the filter, to allow the filter to go fully down before removing/replacing.
I also found and fixed a slight leak from the in door ice maker during troubleshooting. This did not require new parts. This was due to alignment of the icemaker components, which caused water to splash outside the ice maker when filling.