In regards to the seal, you may need to take it to the dealer and let them check it out. Some dealers will work on parts removed from the ATV some won't.
Like I said, I got my 500 for free but am up to over 2K in parts rebuilding it. It is now very reliable and I am pleased so far. However, it is higher maitenance compared to the japanese stuff. How its ridden plays the biggest factor in its continued reliability. I will split this response into two parts: maintenance and repair/riding tips.
1. Mechanical water pump seal - I replaced three of these before I read about snorkeling the weephole and overflow bottle cap. I purchased the seal puller which allows removal with engine cases intact. There is also a small oil seal behind it which should be replaced if it looks crusty. The air space heats up with engine temp, rider goes through cooler muddy water, water gets sucked into air space - trashes seal which leaks coolant out weep hole. By snorkeling the coolant reservoir cap and weep hole this can be avoided.
2. Belt - make sure if there is any mud or crud in the clutches it is cleaned out. This can affect operation and cause belt slippage.
3. motor mounts - make sure they are intact. prone to go out on onlder machines this can cause the distance of your clutches to vary, causing premature wear, creep and slippage of the belt.
4. general maintenance - watch the hub caps, they tend to crack with age and slowly leak out hub fluid. mine was totally seized on right side from running dry. I also updated the jets in the carbs to the new Mikuni parts which made it run a whole lot better. Watch the radiators getting impacted with mud. They are lower to the ground on the old machines and get pretty crappy. Starter solenoid was replaced - they seem to go out. As well as the speed sensor on the right front - this affects the 4wd function.
5. CV Joints - rears have been problematic. Due to high angles the boots/joints take a beating. Replaced inner boots twice so far. OEMs seem to be better due to clearance issues with fwd A-Arm brackets
1. I learned that if idling the ATV make sure it is in neutral. This allows the belt to free wheel and not be spun around the clutches causing hot spots.
2. Below 15 mph stay in LOW gear
3. Above 15 mph use HIGH gear. Both extend belt and clutch life.
Some of this stuff you may already know. The water pump seal and CV axles were my biggest headache.