I purchased an inexpensive ($7.89 including shipping!) FOTASY M39 to m4/3 adapter from Rainbowimaging via Amazon.com. I wanted to try hanging my 50 mm f/3.5 Leitz Elmar and Zorki Industar lenses on my GX7 to compare them against one another and against more modern lenses. The adapter arrived on schedule and appeared to be very nicely made of plated brass and anodized aluminum. I was initially pleased with my purchase. However, a serious flaw became immediately evident. The adapter would not let the Leica infinity-lock release button be depressed. Hence the lens could not be used out to infinity, even though the mount was properly registered from the film plane. I fixed this using a fine-cut flat file. I filed a (file width) notch about 1/16" deep at the seven o'clock position (relative to the red mounting dot). The job took about half an hour. I used a mounted L39 lens to mark the desired location, then removed the inner brass ring and clamped the aluminum part of the adapter down to my bench using hardwood blocks and small C-clamps. I used a fine-toothed flat file (with non-cutting edges) to make the notch. I worked slowly and carefully to make the notch even and smooth. Then I filed bevels at both edges to protect the lens-mount parts. This worked just fine, allowing both my Elmar and Industar to work to infinity. Some photographic results from these lenses will follow, of course. I may even blow a little black paint over my file work.