Boom cylinder rebuild or replace: what to check first

A leaking boom cylinder is not automatically a seal problem. Check the rod surface first: pitting or deep scoring will destroy a new seal within weeks, and the rod has to be replaced or re-chromed before the cylinder goes back into service.

Next, check the pin holes and bushings. Oval pin holes change the geometry of the lift and put side load on the rod. If the hole is out of round, a new cylinder alone will not correct the movement and the bushing should be replaced at the same time.