so i'm thinking i might have a head gasket that is either starting to fail or is already failing.
Background: I've tracked the car 6 times in the last year, driving the car to the track and back home each time, and have ran every session at each event at 100% with no overheating, misfires, any oil/coolant consumption, or any problems whatsoever. I also take the car out for spirited drives about twice a week, sometimes more sometimes less. However, during my last event (November), my overflow tank (circuit sports tank) pushed out about 4oz of coolant, which i accredited to cornering forces pushing it out of the breather/relief port. Since then, the car runs well, doesn't feel low on power, there's no coolant in the oil or oil in the coolant, no smoke from the tailpipe nor does it misfire. It also doesn't consume oil or coolant/doesn't need to have the coolant topped off. But since that November track day, it pushes out about the same 2-4oz of coolant from the overflow tank when I drive the car hard. Either from some sort of denial or because the car has not shown any other ill-symptoms, i've just assumed its from the cornering forces pushing it out. It also never exceeds more than ~4oz. Here's the "test" I did yesterday:

Car was cold, sat for 2 days without driving. Coolant level in overflow and radiator were at the appropriate level. Turn the car over, immediately crack the radiator cap open, and coolant started spilling out. about a half glass full before I re-capped it (i believe this is normal though?). 20 minutes of granny driving, <50% throttle and never exceeding 4k rpm. pulled over, checked the bay - no coolant loss from the overflow tank, and level in the tank was the same as before driving. Waited 15 minutes to cool down, then drove again. 40 minutes of granny driving, same <50% throttle and <4k rpm. Pulled over again, still no coolant spilled out of the overflow tank and level ok. Waited 35 minutes to cool down, then drove again. This time, 30 minutes of hard driving, 100% throttle when possible and 6.5k rpm between most shifts. Pulled over to check the bay, and as expected, about 4oz of coolant had sprayed out of the overflow tank from the breather/relief port.

Only during hard driving does coolant spill out of the overflow tank. There is no boiling, croaking/swirling/swooshing noise from the coolant system when stopped or after shutdown. the coolant system bleeds fine using a Lisle funnel with no bubbles except very minuscule bubbles coming out only when i rev the engine/nothing at idle. Stock temp gauge stays pinned at 11:30/11:45 no matter what I put it through (during all my track sessions and all my street driving.)

Additionally, i have an oil sweat forming around the front and rear driver corners of the head/block mating surface, just as Braineack, Hustler, Joe Perez, patcheko and matthewdesigns experienced in previous threads, which in fact all turned out to be leaking from the head gasket...

I'm a little stumped here.. some symptoms appear to be clear head gasket failure, but the car doesn't drive or behave like it has any issues (other than overflow tank problem). Thoughts??

other info: naturally aspirated, stock cooling system, no ac/ps, have run demineralized water+water wetter for 2+ years. I plugged and bypassed the T fitting coming from the thermo-neck a year ago because it leaked, and routed the line from the idle air valve on the intake mani directly to the mixing manifold line on the water pump, and just recently replaced the OE elbow fitting on the mixing manifold with a brass elbow fitting because that started to leak as well. pictures of the oil sweat from the head are below.