A/C compressor leakage?

I have a 2003 Chevy Impala, and the bottom of my A/C compressor is leaking (Very small leak though). My mechanic says it will be a 600 dollar fix, but I was wondering if there was a way to seal it from the outside without having to replace it. If so, what would kind of sealant would I use? Also, what problems can arise if I don't get my A/C compressor fix? Thanks for all your help, it's much appreciated.