Lintels are load bearing beams which ease stress on the masonry by straddling the top of a window or doorframe. Exposed to the elements, brickwork above openings tend to collect moisture, which can cause the lintel to expand, cracking the mortar.
Caulking or otherwise sealing this brickwork actually does more harm than good as it prevents moisture from leaving the bricks, accelerating the oxidization process.
Lintels can actually be a quick fix depending on the damage. Simply installing steel bars into the existing grout often eases stress on the brickwork. However, if there is enough damage, the only solution is to replace the lintel entirely, removing the existing brickwork and replacing it.
Lintels should only be repaired by experienced individuals like the specialists at Cornerstone Restoration.