I have a 2007 Cooper Convertible, and I am both noticing a very small puddle by the front bumper (passenger side) about 30% of the time. The leak is random. I have added coolant about every 300 miles, as the overflow tank showed near empty. I do not have a service manual, yet, and I have no idea where to look. Any suggestions? What do I have to disassemble (if anything) to check it?

 

Check under the coolant over flow tank, just cause it's dripping on the passenger side does not mean that is where the leak is. If you can put your car on ramps or jack stands, never get under a car that is supported by a jack only!!, take a look under the front and see if you can spot residue from the coolant. There is a hose from the radiator on the pass side of the car, so do not rule out a leak there.
Here is a link to RealOEM.com for the R56 radiator and the corresponding hoses and other related items:
http://www.realoem.com/bmw/partgrp.d...30&hg=17&fg=05
BTW this is an excellent site to get info about how all the pieces go together, you know in case you feel the need to start taking things apart and or adding new goodies!