I have what I'm assuming is a first edition Hayward Navigator. It's gotta be about 15 years old. I inherited it with a house a purchased a couple years ago, and it's worked well. Now, it's getting a bit floaty in the front end. It will run nice and smooth along the bottom, but when it hits the wall, it will do a wheelie and float backwards for 5 or 6 feet, until it eventually reengages with the pool bottom. It also does this when it's running straight uphill from the deep end to the shallow end. It will start slowing down a bit, and the front end will lift right off the bottom. Any ideas on what could be causing that?