They are designed to handle compression loads and can be harmed by simple things such as the chafe caused by lazy running backstays. Also I check how the spreader heel fitting fits against the spar, and whether or not corrosion and friction between the stainless steel pins and the alloy extrusion have weakened the structure. Modern rigs with stainless steel rod junctions at the tips of aluminum spreaders must be checked for galvanic corrosion problems. Covering up these areas with tape and mast boots that trap moisture can be a real mistake. Give the masthead and its associated sheave box a close inspection, especially the welds and holes for clevis pins.
Stretched metal is metal that's about to fail.
Incorrectly installed roller furlers can cause halyard chafe as well as spar damage. Look for signs of scarring and meat hooks in the halyards where they pass over the sheave when tensioned. Check the clearance between sheaves and the side plates, which naturally increases over the years with frictional wear. A wire halyard that jumps the sheave and wedges itself in this slot can be a nightmare to cope with at sea, mandating a trip aloft at the very worst time possible. Check out the area around the mast partners where the mast goes through the deck for any signs of cracking around fittings or holes.