Dual 1219 problem - weak left channel output

Hi Experts,

I have finally managed to get my 1219 going again, this time 
with a new Shure M97xE.
It feeds into a Sony STRAV260 amplifier via RCA cables.

The right channel is working fine but the left one has a 
very weak output. I swapped the
RCA connectors at the amplifier and output behavior also 
swapped, so the problem is at the turntable.

Under the turntable there are four connector prongs beside 
the muting switch. Two of the connectors are between one and 
two inches above the others. The pair closest to the axis of 
the turntable are attached to ends of the RCA cables. One of 
the other prongs has nothing connected and the fourth prong 
is connected to a ground lead that goes to the amplifier 
case and to the shields of the two wires that carry the 
output from the cartridge.

Without taking the arm off, it's not easy to see into that 
area under the shell. Is it likely that there is a bad 
contact there?

Comments appreciated.

RuF