We have a Polaris 500. The rubber things on the outside of the wheels want to come off (one was so loose, it finally did), the hose keeps cracking and needing to be cut off and re-screwed into the hinge-things, I've replaced the part that attaches into the pool, the ball (last summer), two of the "joints", and I think that ball may need replacing again. I took it off, shook it, and it has some water in it. I'm told that this particular Polaris was the wrong size for the pool, because the filter screen in the side of the pool has a tiny mesh to it, and needs cleaning at least every other day, if not daily. Right now, it sprays water from the joints, even though they have been replaced, yet water also seems to be pushing out of the pressure relief button sometimes (in the thing that screws into the side of the pool, which houses the mesh filter). Most bothersome is that the unit itself will not lay flat as it rolls. It angles forward and is vacuuming up very little. It's moving though! Which parts need maintenance, and how often is normal? The pool is only four years old, and we've only owned it for one year. It's our first pool.