why is my coolant draining out?

[chamilka]

Car: 1997 Boxster 2.5 base. 95k miles.
Issue: When attempting to fill the expansion tank with coolant, it quickly drains out through the overflow hose.

Background: During an Autocross event today, I observed coolant leaking under the rear passenger wheel well after several hot sessions. Upon closer inspection, I noticed coolant also steaming off the rear trunk, originating from the expansion cap. The area beneath the expansion tank was also wet, and the coolant tank was nearly empty (95%).

I decided to tow the car back home and tried refilling the tank. However, as I filled the expansion tank, the coolant immediately drained through the overflow hose. I recall adding a small amount of coolant to the tank the day before, raising concerns about whether this contributed to the issue.
note: Two weeks earlier, I tracked the car at a local PCA DE event without encountering any problems.

Considering there had been a recall/upgrade for the tank and cap, I opted to order a new expansion tank kit from Pelican.
Do you think this was the right decision?