Thanks John V. The sump has no markings on the bottom, but does have the blue nut and the finger filter behind it. Engine was rebuilt before I bought the car and I have invoice for a Raceline engine and windage tray, but no sump, so suspect the original 2006 sump was used. Maybe Caterham didn't have markings back then?? Anyway, coupling your advice with my thoughts of "what is the point of a filter if it doesn't filter stuff", I fired it up and went for a blat and all good. I checked the finger filter before firing up the engine, but wasn't expecting anything, as there would have been no flow of oil. I'll check tomorrow and see if the filter has trapped anything. Neil, don't do enough track work to justify DS. Want a Tracksport LSD first!!