Coolant smell, can't find a leak

[BH2000S]

New owner of a 2000 Boxster S with 54,000 miles. Engine was replaced at 29,000 miles, not sure why, possibly cracked head as oil and coolant were listed as mixed on the engine swap receipt that I have from the Porsche dealer.

Car had a dealer oil change and clean inspection 40 miles before I bought it. I've put about 1000 miles on the car, love it, no issues except I keep getting a whiff of coolant, usually with the top down so I don't think it is coming from the AC vents indicating a possible heater core issue. I've been watching the Porsche red coolant in the nice pristine white expansion tank, level does not seem to have dropped. It also does not seem to be using any oil.

Took it for a long drive yesterday, then it sat in the sun for about 5 hours. Started it and my passenger thought they saw a cloud of white smoke from the left vent, I doubt that could be the source, could have been oil in the exhaust that blew forward.

I pulled the engine cover, a bit dusty but no signs of leaks anywhere. I ran it with the cover off, nothing unusual. Exhaust was clear. Not sure where to look next. I'll put some tape on the expansion tank to watch the level more closely.

Anyone have any ideas?