I replaced my entire A/C system last year. It wasn't working so I figured i'd just replace everything that way I wouldn't have to worry about replacing anything on it for a while. I also flushed all the lines and got new orings. Works great now. If you don't want to replace everything i'd at least replace the drier as that should be replaced if you're opening the system. This thread helped a lot:
DIY Complete AC Replacement on 2000 T4R Limited