Isriam,
I have three Dolphins that spend most of there time in the water. One is new, but the other two are older than dirt Dolphin Diagnostic units, that were old when I bought them off of Craig's list. The only time they come out of the water is when I clean the bag or we have a number of people in the pool. One of them failed about a year after I got it because water had gotten into the power cable connector and corroded a pin in half. I took it all apart and found the motor/drive assembly was dry as a bone. Replaced the connector and it fired right up. After about three years, the other one kept throwing a track. I had initially thought the track had stretched and was bad, but when I took it apart to replace the track, the bearings on the drive side just fell into my hand. Replaced the bearings and that one is also back in the pool.
Since both of these units have an unknown history, I can't say whether or not keeping them in the pool is bad for them or not. My personal opinion is that taking them out of the pool, and letting the seals dry out, would be worse, but I have no data to prove that this is true. My new unit also lives in the pool most of the time, but it is only about 6 months old, so time will tell.
I check Craig's every now and again and when I see an old Diagnostic for $100 or so, I always call because just the parts alone (Bag, Bottom door, Cleaning brushes) are worth that to me. I'm looking for another one that I can use as a spare. So far, every one is sold by the time I see the add..
Thanks,
Jim R.