I was flipping through channels today when I saw George Petrie on Leave it to Beaver I don't really watch that show so I was wondering if he was a frequent part of the show or just a one time deal?

He made guest appearances on a host of different TV shows over the decades. You can check places like IMDb to see the extent thereof.

According to IMDb, he only appeared in two episodes of Leave It To Beaver, "Summer in Alaska" and "The Credit Card," both from 1963. As W.B. mentioned, Mr. Petrie made a number of guest appearances over the years, a pretty impressive amount actually. I listed a bunch of them in a thread I made back in February that you may remember, here's the link:
http://www.sitcomsonline.com/boards/showthread.php?p=3479660#post3479660

George Petrie was probably one of the most prolific character actors of all-time.

He's one of only a few actors that appeared in the original Twilight Zone and the 1985 revival. Sadly, He's also one the few actors that died on their birthday.

One reason he was so great was that he was one of the rare actors who would come in on a day's notice and perform like a real pro. You can't say that for many actors theses days. He realy added a lot to the show because he was so well versed as an actor. He could do anything thta Jackie wanted. Props to Mr Petrie!
A friend of mine put up a simple dedication page for him on myspace.
http://www.myspace.com/georgepetrie

George Petrie was probably one of the most prolific character actors of all-time.
One reason he was so great was that he was one of the rare actors who would come in on a day's notice and perform like a real pro. You can't say that for many actors theses days. He realy added a lot to the show because he was so well versed as an actor. He could do anything thta Jackie wanted. Props to Mr Petrie!
A friend of mine put up a simple dedication page for him on myspace.
http://www.myspace.com/georgepetrie