513 Pickups Swap?

Hm, that is strange. I will ask Mr. Fraser, if he provides me direct contact for you.
Just by way of update and a huge thank you to Maertl513 for helping me contact the right people, I received a replacement neck pickup (pricey, but not as costly as I anticipated), which I wired direct to the 5way superswitch. Excellent results with no unwanted noise. The neck pickup is now performing exactly as I imagined it should. Looks like it had been faulty since I purchased the guitar from the original owner.
I’ll just post a warning to tinkerers. When adjusting the height of the 513 (and, likely the 509) pickups, make sure you adjust both conjoined single coils together so that you don’t flex the pcb underneath. If you do, one or more of the six main solder joints will pop. In my case, something more terminal had also occurred deep within the pickup.