Could be that the "end cap" on the 1/4 watt blue Roederstein grid resistors near the socket are shorting to the circuit traces under it....those end caps have a thin paint or some type of coating on them and the paint can break down or chip away and you get a short. Generally those resistors are pulled up off the board slightly or insulated with plastic tubing if the end cap passes directly over a circuit trace but you might want to look at that.
Otherwise, I think replacing the socket with a new one is the way to go.
Steve
Otherwise, I think replacing the socket with a new one is the way to go.
Steve