There are several other posts about the inlet line on the hydraulic pump allowing air to get into the system. I am new to this forum and not sure how to link to them, but look under L3400 postings. I think in this model the power steering has prority over other hydraulic functions which means that the steering maybe the first to show signs of air in the system which maybe casuing the hard steering issue. The inlet line looks to be on the right side of the tractor by the brake pedal from other pictures gat are posted.