Employee was tightening a bolt on Cat D-9 Dozer track return idler that EE noticed had fallen out. While pulling on a wrench, felt a sharp pain in right shoulder. EE continued to tighten the bolt and then went for some oil to put in dozer and when EE picked up a (5)five gallon bucket of oil that had about (4)four gallons in it EE states pain in shoulder was worst.