I learned about about the Model 18 receiver after I picked up a Model 20 tuner.
The 18 apparently has what is basically the same tuner as the 20, including the oscilloscope that can be used for a variety of tuning related functions. If the scope on yours is working that is a good thing. Hard to find replacements.
The Model 20 is thought by some to be one of Marantz' best sounding tuners, albeit not the most sensitive. It is supposed to be basically a solid state version of the 10b. Mine just arrived at Punkers world headquarters at RadioX Towers in Flint for checkup and workup.
AK member Brian knows a lot about this vintage Marantz. Maybe he will chime in.
A Model 18 in good condition is a nice find.