Coolant Expansion Leak - OK to Drive?

[xhifer]

Right after I gave the 986 to a family member to drive 800 miles home, he told me the coolant temp light was blinking.

After diagnosing it, it seems like there is a small crack on the seams between the black and clear plastic part of the coolant expansion tank.

If I keep the coolant level below the Low line, nothing leaks out, but when I refill it to the Full mark, coolant would leak out of the crack and then settle at below the Low mark after the car cools down completely.

He wants to just drive it home and take his time to fix it. I think he should be fine since it's essentially like driving with the coolant bleeder valve open right? Or am I completely wrong?