Linkage bushing are a great place to start, don't forget to check all of them, including the ones that pivot the handles. That machine does not have a hydraulic drive, it's all done with mechanical clutches. You adjust the clutches inside caps on the outside of the frame above the wheels. Clutches would be the next step, they're not real hard to adjust, but you might want to disassemble and clean them first. Mine were full of crap the first time and it made it difficult to get them set right.