ah-the ol oil sight tube....

now this is embarrassing. i have a 07 SD with 27,000k miles on it. every time i change the oil the wiring harness on the left side of the bike next to the battery is soaked with oil and road grime.
i could never find a specific leak and the oil level never dropped. many of you said it was coming from the plug, waterproof grease leaking from it. well i never bought that there was just to much oil & grime for too long a time. so this time id had it. undid all the wiring cleaned it re zip tied it and examined everything. ill be damned if it wasnt the oil site tube!! it was practically invisible because the crack was at the lower banjo fitting facing the inside of the engine (man that thing doesnt come off easy either, i just cut it and pulled it off with pliers). i already had some clear tube in my tool kit just in case.

just cut it off an put the new one on.
I used medical tubing - so far so good.

Take a picture. I have the same symtoms and Im stumped.

Nice find Stratkat. Same problem here since the bike was new. Will be checking that sight tube on the tank- and engine-facing side (nearly impossible to see without a mirror ...).

RC fuel line works a treat,,,,,,,,,and cheap,,,,,,,,,,there's two sizes,,,,,,,you need the larger of the two,,,,,

This is really a weak design element on this bike,,and potentialy dangerous,,,, I have yet to replace mine but I plan on removing it altogether by plugging the holes and I've purchased a "Zeta" adventurer oil dipstick and reading the oil level the old fashioned way,,,gotta remove the side panel but,,,,no chance of oil on me foot,,,or tyre,,,,,,,,,,,,,,,,,,,,,,,,,