I did some research on this on GT, and Ben(of Glockmeister) was the final word. I replaced my guide rod with a steel non-captured one. Reason? They can, and DO, break or wear down enough to tie up the gun. This has nothing to do with wear, or the age of the gun. When the guns were first imported here, they HAD steel rods. After determining the plastic ones were 'basically' functional, and certainly cheaper to produce, the change was made.
My only regret is not buying a captured rod. Even with the stock spring, it can be a BEAR to install back into place after cleaning.
That, and metal sights of your choice would be the only 'must haves', IMHO.