Thanks for the kind words
I think we can say 'leakage' for this one. Whether washing and drying the boards would be a cure is impossible to say.
As to R13/11 (the 100k's) then if you are using a modern tuner or other source then you can go right down to 1k here. That should virtually remove the dc offset problem. It may not be a 'fix' but it is not an outright bodge either and the circuit operation is unchanged. It is just a change in input impedance.
If you try that then remember to upscale the two 330nF coupling caps to maintain the low frequency response. Small electrolytics are fine such as 33uF16v.
Good luck and happy listening.