Air cooled with oil cooler. The four bolt plate on right side of engine (straight in from foot brake) is where I have a leek. It seems that the 500 and 335 has the same design, except the 335 does not have a water pump. So there is a oil seal behind the plate that is leaking. Seems like it is pretty easy to replace. I ordered one last night for 20.00 w/shipping. If you search the internet for a 500 water pump leak, you can find more info on the oil seal. Seems it is highly recommended to replace it if you have to replace the water pump. Not much info on it for the 335. Both are the same though. Hope this helps.
I have 335 (purchased new) and suddenly started leaking in location described above. I removed the 4 bolt cover to inspect the oil seal and found the seal laying in the bottom of the water pump cavern. (No water pump exists on 335 as is oil cooled.) I bought an old 335 engine which wasn't running for parts/ cheap . Removed same cover and also found the oil seal laying inside. Yikes!
The seal (#3084836) is only press fit. There is no E-ring, retainer or water pump assembly to maintain the oil seal inside the arbor. This appears to be a major design flaw in the Polaris engines. Seems the oil pressure at higher PM eventually blows out the seal over time. I pulled and inspected the oil PRV and was within spec and worked freely. Assume this is why the 335 had been discontinued.
This is an old post but felt I should post for information to those that have same issue. Maybe Polaris has heavy stock in oil industry?
I am going to purchase a new ATV soon. Probably go for a Honda, Kawasaki or something else. Seems I find many issues with the Polaris engine designs.