Working on AC Questions...

[Ben Gibby]

Joseph, 
  To answer your questions, assuming the wrench that looked at it is correct, it will be Ok to simply unbolt the manifold and replace the seal.  All the O-rings at the joints need to bee replaced also. Before closing it all up pour some oil into each joint and some into the compressor. You can,t check pressure with a tire gauge, you need the manifold and gauges. A flush will never hurt, it can help find any spots that may have rusted out from the system being open and will remove any water.
  As far as replacing any parts, the drier is probably toast. The orifice tube is most likely OK, but they are fairly cheap so... 
  Your local dealer or FLAPS can tell you the capacity of the system, if you have access to gauges it will help a lot as you should really charge to a pressure not a weight of refridgerant. 


  HTH and Good luck.  
                      Ben