Osborne 1 keyboard repair?

I am trying to figure out if it is possible to repair a Osborne 1 keyboard. The keyboard is made by "Oak Switch Systems" and the type is FTM or "Full Travel Membrane". The problem I am seeing is that 3 keys ("h", "j" and "y") are permanently pressed. I did some experiments with the "h" key. I measured about 20 ohm across the matrix pins for the "h" key. I pulled off the "h" key keycap and the white plastic plunger with the both large and small spring - no change in resistance. I cleaned the now exposed membrane using Isopropyl alcohol - no change in resistance. I applied moderate heat using an electric hair dryer to both sides of the area around the "h" key - no change in resistance. I then used a lab power supply set to current limit hoping to zap whatever is causing the partial short (20 ohm). I slowly increased the voltage and current limit in short bursts until I hit 100 mA before I gave up the experiment not wanting to destroy the two flex PCBs feeding into the membrane. They did get warm but not hot. I have run out of ideas of what else to try. I still measure 20 ohm across the two keyboard matrix pins associated with the "h" key. Has anyone got experience repairing or restoring this type of membrane keyboard mechanism used in the Osborne 1 and probably in other keyboards too? Here are some good and detailed photos of keyboard mechanism: https://www.flickr.com/photos/123564336 at N03/sets/72157644113347562/ Thanks Tom Hunter