I just change my oil for the first time yesterday... everything went smooth... but you should be careful when you're replacing the oil filter cover it has two O rings on it that could get pinched or damaged when reinstalling.
Also like many other 450s there is a aluminum washer on the 17mm oil plug that happen to stick to the motor and fall in the oil pan when I wasn't looking... but luckily I noticed it in the oil pan before reinstalling the oil plug (so be careful).
The manual calls for replacing the O rings during every oil change, but I do not think this is necessary. I personally will be changing them every third or fourth oil change. I do think it's a good idea to keep a pair of them in stock. Just in case.
Did my first oil and filter change after one hour... with regular motor oil 10-40
Second oil change after two more hours... with regular motor oil 10-40
Third oil and filter change after two more hours.... purple magic synthetic 20-50w
from here forward change the oil every 5 to 10 hours (the oil will be relatively clean so I use it in the other motors around the shop lawnmower, pressure washer, etc.)
mine is leaking there too. I dont no why yet but i havnt really looked into it yet. prolly this weekend. Ill post again if i find anything out. I got a recall in the mail the other day too for mine. some models leak fuel from the fuel pump plate at the bottem of the fuel tank.