I have an 03 WR450 and there is a plug (or something missing from just about the exhaust exit on the engine. If it were a street bike I would guess it was the connection for the tachometer. I was changing the oil and when I removed the exhaust pipe I noticed it. Crazy thing is I thought the radiator was leaking, I had it pressure tested and didn't notice this until now. I've only been out once with it like this and every time I stopped I was getting smoke off the pipe and it looked like it was dripping down from the radiator. Now I am sure that it was oil accumulating on the radiator and dripping down. Luckily I was going to run over to 380 and check that out and see if there was still a radiator leak but I figured I'd give her an oil change before going for a run. So does anyone know what went there? If no one knows I will probably just run over to Richardson Yamaha to see if they can help me. The service manual is all hand drawn and I can't find what that was anywhere so I think it was a simple plug.