shurflow 4048 leak

[oldbird]

Hi everyone, its been a while since I've been on, hope everyone is doing well! I've always have liked the shurflow 4048 but in the last few days its been leaking. Right at the bottom of the pressure adjustment screw where the red wire from the back of the pump connects. I'm connected to city water so of course I'm not using the pump now. Tried adjusting it, didn't make any difference. I had a spare pump so I put it in and it was good for a few hours then started doing the same thing. Took it apart and the O ring looks good, no crap in there. I'm stumped, any ideas? Thanks