Hey Colin,
The best way I have found to replenish the oil after a change is to put in about 3/4 of what I know is needed then just keep adding it in increments until I get it where i want it.
Be sure you get all the oil out of the motor when doing an oil change. After all oil has drained out, and you still have the filter screen installed, lean the bike over to the left a bit and KICK it through a few times, this will blow any remaining pooled oil out from the bottom end of the motor, then lean it back over to the right and see how much more oil comes out.
Some advise...........With 186 hours on it, you really should pull the rocker box and check your cam followers. Mine were toast at 180, and hardened bits were coming out and had got caught between the cam follower and the cam lobe causing scoring, I got lucky and the damage was not too severe. You definitely need a cam chain at that many hours, go with the stock IWIS (at least I think that is what it is) chain, it's a good one. AND, put in the updated 2005 cam chain slider that the tensioner pushes against.
I wouldn't worry about the ring, at least from my experience. When I pulled mine down at 220 hours after the right front valve spring broke, the end gap was still within tolerance. I replaced all four valve springs and valves. I also found that the crank seal on the clutch side was toast. Now if that happens you're gonna end up with more oil in the bottom of the crank area. And that's all I found wrong with my motor.
I told myself if I had it to do over again, I would have pulled the motor apart at 200 hours and checked everything out and been done with it. But hey, there are quite a few folks out there with a lot more hours than that on their bikes and they are running great. If you have kept the oil changed, air filter clean, and have not flogged her too bad then you're in good shape. But since you have another bike to ride, for piece of mind, it might not hurt to pull the 04 down have a look and keep on trucking.