Got a minor oil leak somewhere on the right side of the engine and I can't tell where it's coming from.  I checked a couple of obvious (and easy) candidates, the oil fill cap and oil pressure sensor, but those don't appear to be the source. Anyone have any tricks for isolating an oil leak?  I've wiped down the engine as much as I could, but the bike is 15 years old and I'm not a meticulous cleaner of engines...  I'm imagining wrapping tape or paper towels to suspect areas and riding until a wet spot appears, but that doesn't seem very reliable.  Wondered if someone else here had dealt with the same problem.

How much oil is leaking? If you park the bike overnight is it enough to make a spot on the ground?

Thoroughly clean and dry the engine, then use a small paint brush to dust the areas around any suspected oil leak with baby powder or flour.  After your next ride, the source of any leaking oil will be evident.

After riding for an hour the side of the engine is fairly wet with oil and it will leave ~5 drops on the floor.  It only leaks when the engine is running.  One possibility is a leak from the line connecting the engine to the oil cooler.

So I need to thoroughly clean the engine?  Well, I guess if I have to...

Ian wrote:
 One possibility is a leak from the line connecting the engine to the oil cooler.

So I need to thoroughly clean the engine?  Well, I guess if I have to...

Well, you don't really HAVE to... That would just make it easier to locate any/all leaks.  If you suspect the oil cooler connection, start there.  Wipe it off and  sprinkle some powder.  If that's the only leak, you're golden.  Fix it and go for a ride!  ;-)

Come on...it's time.  Your ride has been patiently serving you with Italian beauty and funny desmo sounds as it takes you down those favorite twisty roads.  Now she has a bleed when she does her job and you're hesitant to clean the engine.  "Well I guess if I have to." Really? "If you have to..."  My friend you get to.  You get to tenderly pull aside debris and lovingly wipe away the stains of spilled life keeping blood from her.  You get to do this while talking to her and assuring her that she will be okay and that you love her and you are there for her.  YOU GET TO!  Ian, if you fail, someone may come along and woo her away from you and leave you looking for a Honda to abuse.  It is time to repent, my man.  Pray to the good Lord above that He may grant you repentance.  

Ulywood LAUGH!  Well said, Sir!

Touche! 

I have heeded your wise counsel and have spoken kind words to her and rubbed her belly.

It might be the weekend before I get some proper cleaning supplies and pinpoint the leak.  Still hoping it's something manageable.

I'm sure you're all dying to know where the oil was leaking from, so here you go...  It was the seal on the layshaft, which sticks out of the right side of the engine and spins the pulleys that drive the belts that open and close the valves.  There are covers over the belts.  After the engine had been running for some time, oil would begin seeping past the seal and by the time it started seeping out from under the belt covers it was crawling around the side of the engine and, thus, was hard to isolate.

The seal has been replaced (along with the belts and their bearings, because it was time) and all is well.

Ride on!

Excellent!