Booster line seems to be in good condition, definitely not original, nothing obvious that I can see.

That said, this only happens once the car is warmed up and in sub-mid 70s temps. That engine is HOT by the time it hits operating temp. What possible effect could the cold air outside the car have on the vacuum lines. Even if there were leaks, the engine bay temp is the same in August as it is in December when the cars warmed up.