@gibi:
make a plug of some clean paper-towel. plug the "hole" you were referring to (called
drainage outlet passage) and inspect it after a while/ride... see how much oil and/or cooling fluid the paper collects.
it is not abnormal to have a few drops every once in a while. it is due to the expansion/contraction of engine's parts.
-drainage outlet passage is exactly what it says-
the water pump is located right there. it's shaft and impeller have a few seals. there's also a ball bearing... to make it simple, on one side of the crankcase you have oil, on the other you have cooling fluid. because the parts expand and contract at different rates, the seals may leak a drop of oil or cooling fluid. the drainage outlet passage is located such that there is no contamination between oil and water and vice-verso... my understanding anyways.. ;]]
*if the mechanical seal for the cooling fluid is bad, replacement is relatively simple. on the other hand, if you have lots of oil leaking, the crankcase needs to be split in order to replace the oil seal.
** post your questions on the main Vulcan900 page. you'll get faster and more responses from the 'pro' guys. link:
http://www.vulcanforums.com/forums/forumdisplay.php?f=49