Pinpointing an AC Leak

[JKAMOCSAI]

Working on a 560sl AC. Quick background: AC was not working for about 2 years. Decided last month to charge it . It took the charge, and was working well. The other day while highway driving it got extremely cold, and the fan speed started slowing down, almost to a halt. I turned it off, and let it rest. It worked later that same day, and then two days later it was kaput. - no trace of freon in the system. I believe the evaporator froze, and stopped the fan from turning.
I then decided to charge it, and check for leaks. After juping the low pressure switch I was unable to get the compressor to start, so I jumped it with a 12V source, and put 2 cans of freon and dye in the system. Nice and cold for a while. No trace of dye anywhere, but my sniffer (electronic) sensed some at the front of the pump. No trace in the car, and a possible trace near the evaporator.
I solved the electric problem with a new relay, and I also changed the ETR switch while I had the glove box out. Now the compressor engages when the pushbutton is used, like it should.

My question: I have now tried to vacuum the system down, and it won't hold a vacuum for more than 10 minutes, however it did hold the freon for quite a while on the high pressure side, but not on the low pressure side. The vaccum also drops more quickly on the low side.
Since I can't get to the Evaporator, (the 87 560 sl car was built around it), I'm stumped as to what to attack first. Should I go for the compressor- and see if that solves the vacuum leak/freon leak, or try the expansion valve or evaporator before that.
If it holds the high side longer, does it indicate where the leak is?
Is it possible that the faulty relay and ETR caused the compressor to stay on, and freeze over the evaporator, resulting in the compressor seals to be damaged. I'm wondering why I can't locate the leak with the electronic sniffer unless there is a high pressure on the system, but yet under vacuum the system leaks down very quickly. Any suggestions would be appreciated. Wish there was a way to isolate out the evaporator and expansion valve to do a vacuum test on the rest of the system.