I was just looking back at the schematic and OP - I see that you reported Q11 was bad and replaced, but not with the same type. This could be the problem, since JFETs all work more or less the same, but can vary greatly in characteristics. Check the Idss spec of your replacement versus the original type. It could be that Q11 simply can't cut off far enough with the available negative gate drive from U2. If you don't have the right one, or one close enough, you can help it out a bit by adding a shunt resistor from the gate to -12V, to drop the gate more, then U2 can lift off the rail and get control of the situation. Another option is to temporarily add a diode or two in the source lead to lift it, and help cut off. You should put the same or a proper equivalent part in once it's figured out.
Ed
