JD X300. My 81 yr friend has his 78yr old wife mow with their JDX300. He asked me to help fix a stuck deck lock. Seems that the weight of the deck will not let the deck lock to be pressed down or pulled up. nothing seems to be in the way of the linkage above or below. I depressed the left foot pedal completely. With much pressure I was able to move the deck lock down and up. I lubricated the linkage liberally. I operate the deck lock many times with a-lot of pressure - more then the 78yr old lady could exert. I then adjusted the mower deck level. I tried to press and pull the deck lock again and it would not move - locked up again. Please help me help this elderly couple. TY