Same here, kinda hard to believe the whole system (minus inside coils). The only time you have to go this far if the compressor itself burnt out. If the compressor burns out, you would have to find out why. Usually comtaminated freon is the main cause due to leaks or something. Since you went this far into repairing the a/c, I would inspect your condenser coil (located in front of radiator) and make sure it is not pitted too much from road debris. If the condenser is beaten up pretty good, I would highly recommend you get this coil replaced. Else you may revisit another complete rebuild in the future.
I don't believe in any kinds of additives to put in a freon system to make it quieter or run smoother, etc. never been proven, just like most of those other oil additive for your engine oil. Most of them don't work.