a sweet smell

I doubt that you have a leak at this point if the dealer had the tester on it like you said for 45 minutes. That would show any leak as the pressure would drop. Some times if you have the A/C on, the condensation on the evaporator core will produce a wierd smell. Although the Prius core is treated to resist mold and mildue. Some people are more sensitive to that smell. As a test next time shut of the Auto feature and set it for out side air and fan on medium for 3-4 minutes before you pick up your brother and see if he can still smell it. I'll bet not. Worth a try.

 

Perhaps the pressure would not fall all that much with a pin hole leak, even after 45 minutes. Did you tell them what the problem was or did you just ask them to check for an antifreeze leak?

Who was it in PC who works as a Prius mechanic, maybe Galaxee's husband?

 

Like Foxy said, it could be a pinhole leak in the heater core. I have had this happen to me on several occasions in the past with other cars.

 

any leak will drop the pressure I can assure you of that. 39 years as a mechanic I've seen them all from hoses to head gaskets and every thing in between. Including rusted cylinder walls from the coolant side to pin holes in exhaust ports in cylinder heads. Pump the system to 10 lbs and wait, any leak shows eventually.