inless you want to do some cleaning by hand with, say some rags, small brushes & 'brake cleaner' you'd do best to leave it a 'little grimy' avoid using 'GUNK' & water rinse on any '85 or newer BMW engine, especially a 750iL.
+ + + DO NOT HAVE IT STEAM CLEANED ! ! ! ! ! ! !
the moisture will get into places a things hard to access and easy to damage. just give it some 'elbow grease' and smile when your done.....jb