Air Conditioner System Repair - 300SD

[nyko46]

My Mercedes 1982 300 SD is in need of a repair in the air conditioning system which probably I was the cause for make it worse last time that I ad refrigerant.
Previously it was slightly leaking and after a year all refrigerant was gone.
At the end of April 2011 I was adding 134 A to the system but I also put in the system 6 oz of stop leak which caused my system to stop work completely.
I ordered new parts to have it repaired using the DIY method but as I also found that the system still leaking and I do not want to put new parts on it before find and repair the leakage. I have no much idea from where to start checking for leakage and do not know which will be the best and cheaper way to perform this check obtaining the best results. After find the leakage I want to repair it and then go to the next step of clean the system and then start to installing the new parts. I have ordered new Receiver Drier/Accumulator, Expansion Valve, High/Low Pressure Switch, and a kit of Seals.
I also do not know if the stop leak had or not affected my compressor but I know that the compressor should not be cleaned or flushed.
I was informed that to flush the system I will need to use shop compressed air but not informed what is the minimum or maximum PSI required to have it properly flushed. Should I change my compressor oil after the system cleaned and flushed? If leakage is in some area that accept soldering should I solder it? How to flush the evaporator without removing from it's location?
I will need your help in order to accomplish this task and I will be more than happy to hear from you.
I have mine and my wife Mercedes to get this repaired and Texas is very hot during the summer season.
I appreciated your help.
Thanks.

Nyko46