Dunkirk Propane Boiler

We are looking into purchasing a home that has a Dunkirk (propane) boiler (with which I am not familiar).  It's 2 years old at present.  Any helpful comments, opinions, experiences, etc. regarding this equipment would be appreciated.  Secondly, our Inspector (Joe from Houseworks) noticed a layer of what would best be described as an oily film on the floor of the housing.  There was not a great deal of this substance present, but certainly enough to be noticeable.  If anyone has any insight as to what this stuff might be and whether or not it may be indicative of an issue with the equipment, your input would also be appreciated. Thank you.