Once you've found any and all breaks in the membrane circuit, get your conductive paint and shake it well to mix the solid silver with the solvent.

Use a thin brush or a cocktail stick to apply a small, thin layer of the paint right over the area(s) with the fault you located. If you have a dip pen this will work even better.

Allow at least 24 hours to dry.

If there are gaps in your newly applied paint, apply a second coat and allow another 24 hours for that to dry.

Now check the same area with your multimeter. If it's worked, there should no longer be a fault. So grab a drink and celebrate! That's the tricky stuff over. If it hasn't worked, use your multimeter to find the exact spot where the track is still broken and add another layer of paint.