hi and cheers for the info.
The solenoid is about an inch in diameter and held down by two star headed bolts.
I lost a fair bit of oil and its all over most of the bottom of the sump - at first I thought I'd banged the sump or sump gasket had gone. If I start the engine I'm losing a teaspoon of oil per minute from the solenoid you mention. Suspect it unlikely to lose oil from the solenoid and sump all of a sudden, so I'm thinking that the oil from the solenoid is running down the back of the lump and pooling/spreading along the sump gasket.
Thats the thinking anyway... so I'll replace the solenoid and put up another post if that sorts it.