Toyota Repair: Sienna 2000. A/C, freon leaks., uv dye, freon

Question
I have to fill up A/C system with new freon every 4-5 mths. Mechanics can't find the leak, even with the UV dye. Which part of A/C could be the the most likey suspect ?

Answer
A common leak if it has rear a/c is the connection at the freon line that connects the front pressure lines to the rear a/c evaporator, these lines can be inspected from underneath, the leak is normally visible at the connectors near the front, I can't say that this is the case but I'm just saying that they have a tendency to leak there and the remedy is to replace the o-rings on the leaking freon line, I have done this many times and if you like I can send an illustration locating these freon lines that have the problem, please provide an email address if you need the illustration.