I now have my infinity focus spot on but it was not easy. I purchased four 1/8" retaining rings-External Copper Plated at Lowes. They are .25mm thick. As it turns out that is slightly too thick but it was the thinest smallest I could find. I then used my Dremel tool to grind away some of the metal from the back of the flange at each of the screw hole locations. I placed a retaining ring at each screw hole, carefully lowered the ring in place and screwed the 4 screws in slowly tightening but not too tight and testing how smoothly the lens turned and locked. I then took pictures at infinity and compared them to pictures I had taken of the same subject when I manually focused for infinity prior to any modification. I took shots at f2.8 and f5.6. It took several iterations of removing the ring, grinding some more metal off, reassembling and testing again. Before the modifications infinity focus showed 10' on the lens barrel and now it shows infinity.
I almost thought I was there when I was getting sharp images at 5.6 and slightly softer images at f2.8 but further tweaking and comparison with shots taken when it would focus past infinity convinced me I wasn't quite there and sure enough, further tweaks got me right on so at f2.8 it looks very sharp just like at f5.6 for the same distant object.