I bought a used 1023e w/ 60" mowing deck last year. when using for first time after about 20 minutes the engine bogged down and would hardly move. turned off PTO and ran fine. I rechecked hydraulic level and it was way over full and foamy. WATER! drained the system replaced filter and cleaned suction screen. it then took about an hour before it lost power. drained and replaced everything again... and once again. no evidence of water but I couldn't run mower for more than about an hour. took it to dealer, they could find n problem. still having the same problem. sometimes I can't get an hour before it starts losing power. I have about 9 acres to mow. I can't do it an hour at a time. I have performed all services recommended. any ideas?