[MrFixr55]

HI DConat,

It wouldn't hurt to put a 0.01 uF cap between the deck and volume control.  However, there is a 0.01uF cap between the wiper of the volume pot and the grid and another between the high end of the pot and the signal from the radio.

Attached below is a section of the schematic showing where to break the audio connection to add the Radio-Aux switch and aux jack, and a schematic of the switch connections:
   
   
Switch shown in radio position.

You could connect the jack to the switch through a 0.1uF cap if desired.  If the device that you wish to connect is stereo, a stereo to mono "Y" adaptor is required to hear both channels.

Hope this helps.