Gtpulse
Dyna-Tech Fan
Think I’ve got it sorted - I think there was a thread damaged on the cup, I thought I had tightened it fully but was not. Removed it, degreased and ran the lock ring back and forth on the full width and it cleared a damaged part of thread. Managed to get the lock ring cinched down tight now. Not sure if a pin spanner is the correct tool for the cup but neither the Suntour nor Sugino bottom bracket wrenches I’ve got would fit the cup part.