If your valve stem seals are worn and leaking, your valve stems and valve heads can be wet with oil film residue instead of being dry.
On the exhaust valve, the oil film can get carbonized from the heat and build up on the valve head if heavy enough.
You might be able to look down into the intake port to check the intake valve.
Unfortunately, about the only way to check the exhaust valve is to remove the exhaust headers and look into the exhaust port.
If the stems seals are shot, the two ways to replace them are to either remove the cams and heads, the use a valve spring compressor to remove the springs and replace the stem seals. Then reassemble.
The other method is to remove the cams and spark plugs, then use compressed air to hold the valves closed and use a special tool to compress the valve springs and remove the collets, the replace the stem seals and reassemble, all the while using compressed air to hold the valves closed.
Either method might prove to be difficult to do with the engine in the frame (especially the front head, due to the frame and steering head proximity).
It may require engine removal to complete the jog. Not insurmountable, but a pain in the butt, and requires special tools to remove and install the swingarm pivot and adjust bolts, and engine mount adjust bolts (if an SP1).