Vintage Synth Repair

My SH-101 was in worst shape than I thought: broken copper traces near  
one of the keyboard matrix connectors. Reflowing the solder joints  
didn´t do any good as it quickly melted the phenolic (or whatever 
material is the PCB made of) and the traces jumped off. 

As the keyboard contacts are of the conductive rubber type, the copper 
traces lead to what seems like conductive carbon ink pads, so there´s 
nothing solderable to run "oops wires" from. 

One possible solution might be removing the varnish at the connector 
end, exposing enough solderable copper area. What can be used as 
solvent?

There is also one special silver ink pen that I could use to redraw new 
traces directly from the carbon pads, but how well would the ink bond 
to the pads? I coudn´t measure the carbon´s resistance, let alone any 
signs of continuity... 

Do you know of a more conventional way to do the repair?

Any advice would be greatly apreciated.