The oil pressure connector can be prone to water ingress, a mates GS had a temperamental oil pressure warning when wet. Might be worth a squirt of WD or similar on the connector.
My old 2004 GS had issues from build in summer stop/start traffic with oil warnings using 10W40, solved when BMW changed to 20W50 for oil servicing in 2006.
I dropped in a liter of 20/50 at last interim fill - its going fully 20/50 when the full service is due