I think I blew the head gasket on the track. Oil and coolant spray around the engine. It was interesting that I only noticed something was wrong after I got off the track, and the car was idling very rough and had a rattling sound. On inspection it seems to be emanating from the top end. Plug 1 is oil fouled and there are cyclical puffs of smoke coming from the oil filler tube/aos. A review of my in car video shows that although I lost 2 litres of oil, oil pressure never dropped below 3-4 bar. Engine oil maxed at 120c and water temp never got over half way.

I haven't had time to look at the cylinder bores (writing from the airport) but I'm guessing the noise is a result of a lifter not getting oil due to blown gasket. Seems weird that there was no noticeable drop in power on the track.

Does my hypothesis seem reasonable?

 

No smoke from the exhaust pipe?

 

No smoke noticeable on track, but noticeable once I got back o the pits.