This information has kindly been provided by Ballenger Spar Systems, Inc. This company has been producing the highest  quality racing and cruising spars for thirty three years. This is an extract from the full article:

The single greatest cause of sailors becoming power boaters is the lack of maintenance given to their spars and rigging. Many sailors simply sail their boats until the rig falls down

Both rod and wire rigging have finite lives. They both fall prey to fatigue and corrosion over time. Wire rigging due to its construction and method of attaching fittings will probably fail from corrosion where as rod riggings' nemesis is primarily fatigue.

The current trend in halyards is away from rope to wire halyards and toward all rope halyards. The rope halyards are usually lighter, and more kind to hands and the mast. They are, however, much more prone to chafe than wire halyards

Down the complete article "Rig Maintenance" HERE

This is also an extract from an article by Buzz Ballenger - the full article is available of the Ballenger website - see link in right panel of this page

1. If the tip of your mast seems to fall off, and your uppers are fairly tight, try loosening the intermediates.

2. Check the rake of a mast by tying a heavy object to the main halyard and measuring the offset from the back of the mast. Subtract any sheave offset present.

3. Make sure to do the final tuning of the mast when sailing. Make sure that the mast remains straight athwart ships. Check that the mast bends forward in the center (the reason for prebend).

4. Check to make sure that the bottom of the mast is square athwart ships, and for a keel stepped mast that the mast is straight through the deck. If it is not, the mast will be forced into an S bend that is impossible to tune out. We usually tune a keel stepped mast with the deck chocks out and shim the mast sideways after the mast is straight athwart ships. Mast steps and mast collars are rarely exactly on the centerline of the boat.

5. Use a steel tape run up the pole lift or main halyard to get the mast vertical in the boat.

6. Always pin and tape turnbuckles and cotter pins after tuning. Be sure the cotter pins are taped so that the sharp ends are covered to protect people and sails.

Well, there it is, twenty-five years of experience condensed into one and one-half pages. Now you should be ready to tackle tuning any mast. In fact, I hear there are some openings for riggers for the next America’s Cup.