Repairs Derby (Ferris) zt2354 hydraulic problem

Hello all! I am new to the forum and I appreciate the information I have found so far. I am working on my aunt's Derby ZT2354 (Ferris) zero turn mower and am looking for some advice. At the start of the summer the mower was working great but one of the hydraulic hoses going to the right wheel motor was leaking (it has 2 pumps and 2 wheel motors but 1 reservoir). I replaced the hose and now cannot get the air and topped off the fluid with 15w50 mobil synthetic (what it calls for) and mowed about 100 yards and the right side quit working. I opened up the bypass relief valve and followed the book instructions to purge the system to no avail. I have tried bleeding the line at the wheel motor and also changed the hydraulic filter. The left side has worked perfect all along but the right is still not working right. Does anyone have any ideas? I have checked the suction hose and is good and I have pressurized the reservoir with air also. I don't know what else it could be. Any ideas?? I replaced the other hose on the same side a couple years ago and had no issues whatsoever. Thank you in advance for your help!