This post is address the most common and generally easily fixed Vulcan 1500 and 1600 oil leaks. (Vulcan owners seem to take minor leaks more seriously than Shovelhead owners.)
Spark plug tubes. Front cylinder tube is on the left side and rear cylinder tube is on the right side. The camchains get stretched a bit and cut the sparkplug tubes or the tube o-ring seals may be cut. The oil runs out the rain water drain of the tube. The tubes can be replace or repaired with JB Weld or similar. More on camchains extenders and sparkplug tubes; here, here, and here.
The next two pictures were sent to me when I was trying troubleshoot the leaks for other folks.
This is how a rear leaking sparkplug tube looks.
This is how a front leaking sparkplug tube looks. The white stuff is spray deodorant to help track down the leak.
The rear cylinder drain hole is easy to see. Here how to get a good look at the front one.
Camseals. The little black circles have covered by the chrome rocker covers. The front cylinder plug is on the left side and rear cylinder plug is on the right side.The dealer will want to plug the motor to fix this leak. However many people report good results by cleaning the area real well with brake cleaner(careful around paint) and then filling the gap around the camplug with black RTV silicon.
Clutch pushrod seal. This usually manifests itself as leak dripping off the kickstand mount. This how I fixed mine.