If the resistor only feeds 0v to terminal 4 then you can bridge it out and use three wire sensor.
yes I can confirm that the resistor only feeds terminal 4
well I've atempted to trace terminal 6 the best I can, it leads directly to pin 2 of the socket at the top of the board then the track is obscured by the counter thumb wheels that also has components mounted beneathOK, It looks like the original sensor was a simple n-p-n phototransistor, but because base was unconnected (no external bias w.r.t. emitter), it could be used to pull-up the voltage at T6.
For the new sensor, n-p-n output generally used to pull down a node (T6) to 0V in conjunction with a pull-up resistor.
So p-n-p output could be used to pull up a node (T6) to 15V in conjunction with a pull-down resistor - I think this is what you need..
Since you have the p.s.u./relay module apart, can you confirm a pull-down resistor on T6?
and being a double side pcb I've lost track (pardon the pun)
If it helps the resistance reading between T6 and the negative rail when the module is re-assembled is 3.1k