If you have oil between the modules, you have a leaking seal on one or both of the two modules.  Each module has its own oil and it should be dry between them.  It is very easy to replace parts on those.

edit to add:  I would not just replace the broken bolt.  I would unbolt it between the two modules and check the splined shaft that connects them and replace any leaking seal.  We just rebuilt one of those cutter bars.  Our New Holland service guy said when you rebolt them together, you tighten the threaded bolts to 50 ft pounds, and then add one complete turn of the nut.  When ever we open one up, we tend to go ahead and replace the splined shaft while in there.  That is where you get your slack between the units as it wears.  It is all very self-explanatory once you tear into it.