Fixin' the Fishin' Gun
Over time, the action of the pistol had accumulated soot, grit, and grunge. Some of this was caked on the sear. Once the coating was caked on the sear, the fine adjustment that I had on the over travel screw was not quite sufficient to always drop the hammer. Admittedly, I likely contributed to the problem with my habit of applying a smidgen of Tetra grease to the sear. 95% of all gun problems are related to the gun being dirty.
A good cleaning of the pistol cleared up the problem. I stripped the Ruger to the point shown here, and used brake cleaner and stiff nylon brushes to loosen all the grunge. Then, I reassembled the pistol and readjusted the over travel screw for a bit more play. Finally, since I now had the screw protruding from the face of the trigger slightly, I filed it down flush and repolished the trigger face.
One of the best online resources for field stripping the Ruger MKII can be found here. If you are inclined to detail strip the pistol, this page will help. Enlarge the photos to guide you.