I've done it twice. I had some really bad luck ordering things from the states so I decided to shop around. France, Spain, and German Ebay have really good deals also. Especially if you are looking for used transmission gears, or a cylinder. Deals everywhere!
By adding more oil you are effectively leaning the fuel mixture out. More oil= less gas= lean mixture. That is why the bike seems lean. Take out the gas/oil mix that you have in there with the extra oil and go back to the original mix. Then I would either move the needle to the 3rd clip and try...
You'll still have drag as that is how the clutch is designed to operate to keep the drivetrain loaded. That way its less jerky in the super tech stuff. It'll be much more manageable though.
For the clutch drag put in some GM Autotrac transfercase oil. Everything else I tried in my 02' 280 Pro made the clutch drag. As for the oil coming out? I don't know about that one. The oil you put in seems better suited to an enduro bike.
I did exactly what this guy did in my wife's 2001. Get yourself a cheapo crf450x Rekluse and follow the instruction in the video to a T. https://www.youtube.com/watch?v=LsqKrh8fmZk
I just went through this on my XC200. Just get the CR250 rod kit and have your local bike engine re-builder take care of installing it for you. There is a place called Cycle Therapy in Bellingham Washington that did mine in one day.
The bearings on the transmission shafts are probably worn a bit. Next rebuild buy all of the bearings and replace them while you have the case split. Another question is what oil do you run in the transmission?