First thing, don't panic. The refrigerant gas used these days is no long a CFC - those were the gases that remove ozone from the upper atmosphere.
I've had issues with main dealers (Volvo, not Lexus) in the past with a leaking air conditioning system. They concluded that because they could hear bubbling noises from the evaporator (which is normal) then there must be leaking going on. No check with ultraviolet. I knew they were wrong, and took it to a specialist, who checked with ultraviolet, and sorted out the real leak very quickly, including vacuuming the system before refilling.
There is some lubricant in with the refrigerant. This is absorbed by the O rings in the system, and this keeps the joints tight. That's why, even if you don't use air con in the winter, five minutes use every month is a good thing.
Incidentally, using air con in the winter dries out the inside of your car, and keeps it that way. I recommend it. : o )
Good luck.