I completely agree with Jim. Same thing happened to me a few years back - a leak showed up. We patched it once, and it held for a year or two, then another leak showed up. The HVAC company recommended replacement of both evaporator and outside unit, AND the tubing connecting them. We did, and took the opportunity to put in a heat pump.
By the way, when you do replace your outside unit, spend a little more and get a "scroll" compressor. MUCH quieter than the other kind, and I think they last longer, too.