I have managed to completely disassemble the bad Osborne 1 keyboard - remove all key mechanisms (body, plunger, main spring and actuator spring), remove the 3 layer membrane from the aluminium backing board and separate all three membrane layers (bottom, spacer and top) - all without damaging or losing any bits. I then carefully cleaned off all adhesive and other sticky gunk from all layers using various solvents including water, isopropyl alcohol and white spirit. The silver tracks remained undamaged as confirmed with a multimeter. I then carefully reassembled the 3 layers, inserted and super-glued the keyboard mechanisms in batches, testing after each batch. I did not use any glue to reattach the 3 membrane layers so they are held together only by the keyboard mechanisms with their prongs protruding through the layers into the aluminium backing plate to which the prongs are super-glued. I sealed the edges around the membrane using Kapton tape to provide protection from dust etc. The tape also attaches the membrane edges to the aluminium backing plate. All keys except the "Alpha Lock" key work perfectly. It appears that I have damaged the address line 7 on the bottom membrane. I can live without "Alpha Lock" so I did not pull everything apart again to fix this un-important key. The conclusion is that membrane keyboards can be fixed if your life depends on it. It is absolutely uneconomic though. I worked about 30 - 40 hours on the keyboard alone. Working Osborne 1s sell for between US$100 and US$300 on Ebay.
Regards Tom Hunter