This may be an off the wall suggestion, but don't refrigeration supply houses sell a small "line tap" that is used on window A/C units?
I bought one several years ago to repair a leak in a window unit. I lined it up with the small pin hole leak, screwed it in place and tapped the line where the leak was located. The line tap also included the fitting for recharging the A/C unit. After fitting the tap I recharged the unit with R-22 (I think, it's been a while) and it worked for another 10 years. Let us know how it works out.