How can you tell by looking at a sear if it's time for a replacement or is a little damaged. I'm going to check out my buddy's 1911 tonight and his gun seems to fall to half cock sometimes. It's a used one he bought recently.  Will it be worn out and if it is a new one can be bought and replaced right?

If it falls to half cock sometimes the worst case scenario is some bubba tried to do his own trigger job and screwed it up.  What else did he screw up?  If it's just the hammer and sear engagement surfaces you can put new ones in for about $40 on up if you do it yourself, which isn't hard.  Just don't screw with the engagement surfaces w/o knowing what you are doing.

BTW my hammer and sear I got from Wilson came all set for install.  I research sear angle and engagement planing on working on it once I received it, but the angles and engagement were exactly as they should have been.  All I could do was make them worse so I left them alone and have an excellent pull as a result.

Kent

There's only one way to do it right.  A qualified 1911 gunsmith will look at the engagement surfaces with a microscope.  The hammer and sear are put on a jig that is designed for this.
Bring it to a 1911 gunsmith.