second surgery for aortic stenosos

Hello, I am a 48 year old female with congenital subaortic membrane stenosis. I had surgery six years ago, and now it seems as though I may be facing a second surgery. My peak gradient was 105 at the time of my first surgery, now it is 66. I am doing very well clinically, pretty much the only sympton I have is excessive sleepiness. Of course, this may be from getting up at 4:30 am on work days. I have a few questions, the first is how high does the peak gradient have to be before surgery is necessary? Also, if a person is pretty much asymptomatic, can surgery be postponed until symptoms begin? Also, I excercise regularly, wallking on my treadmill 30 min. a day 3 or 4 times a week. My cardiologist says this is fine, I would just like a second opinion on this. I walk at 4 mph and work up a pretty good sweat. I do not seem to have any problems with this, just do not want to put myself in any danger. I also work as an office manager and am generally active. Thanks for taking the time to put my fears at ease. I also failed to mention that I have three leaking valves, not leaking enough for repair.