All good solid advice!
I have worked on my own and my son's vehicles over the last 15 years, and virtually all of them are or were R12 systems. We did out AC license too!
My son has actually back converted his 1987 Mercedes 300TE from 134a to R12, and used the later E320 larger condenser/twin fans to boost his AC system for use in Az... He says it works far better than the original and the 134a conversion now.
1/ If you are looking for info on your basic system, look no further than the relevant model years of GM C or K trucks.
2/ All the system I have done so far, the issue was the 99.9% the original O rings leaking... of course, that meant a new dryer, and maybe orifice valve for surety.
4/ I have always started with pulling a Vacuum on the empty system... its free, and sometimes tells you a lot for nothing! Hear the leak... awesome... after that, I have also used my compressor to pressurize to find other leaks with a length of tubing to my ear.
5/ Replace EVERY O ring in the system joints... with HNBR units. I bought a Metric and Imperial kits and it has covered EVERTHING in my garage!
Cheap too.. Example.
6/ Once the new components and rings are installed pull the max vacuum you can do with your pump and see if it holds for 24hrs...
Here is a couple of pics of the revamp I did on my now sold 1991 Mercedes 190E...
Compressor reseal with HNBR green rings visible...
After recharging with R12, it would output 35f air at 2000rpm with ambient air at 90f!
For years later, the new owner says its still ice cold!
I was lucky to find this on Craigs List for $200, so now, I am completely setup!