My Bostitch pneumatic nailer/stapler is leaking air from the exhaust area. What are the most common causes?

The parts that are causes for air leaks from the exhaust are listed below from most common to least common: 1) o-ring on the inside diameter of the head valve piston 2) o-ring on the outside diameter of the head valve piston 3) cylinder seal 4) head valve piston 5) cylinder cap 6) cylinder sleeve -- check the area where the cylinder seal seats on the cylinder sleeve Note: the o-rings and seals are included in all o-ring/rebuild kits, or the individual parts can be ordered separately. See Service Parts posting on this site.