Any hints on a/c seal replacement?

["K M" <symbiotic@hotmail.com>]

I need to isolate the compressor and replace the seal because it is leaking. 
  I have the service manual and can follow it.  I am just asking whether 
there is anything special that I should be aware of and just what seal does 
this use (and where is a vendor).  I am somewhat surprised that this 
compressor can be isolated without losing the freon charge. Anyone have any 
experience on this? Oh, I am licensed to buy and use r-12 so that is not an 
issue. Thanks, Kim.