It's a $4 and 15 minute job so why not stop that drip.
Also some say you don't need to drain the oil but I prefer to do all my maintenance at one time at one time so that means oil change and tappet and cam chain adjustment too.
1. Drain the oil.
2. Remove the shifter lever clamp bolt and (taking note of lever height) slide shifter lever off of shaft
3. pry out old seal with screwdriver or hooked scribe, being careful not to scratch or damage the shaft or the engine housing.
4. Cover shaft splines with tape to prevent damage to new seal.
5. Oil new seal.
6. Slide over shaft and press squarely into housing. My seal pressed in with only hand pressure, but you can use a deep well socket and give it a little tap if it's stubborn. Just make sure that it's going in straight!
7. Reinstall lever and bolt. Pay close attention to the height of the lever when you put it back on, and follow your shop manual's torque spec for the pinch bolt. (You have a manual, right!?)
8. While you've got the oil out, go ahead and replace the oil filter and drop in some new oil. You're done!