Hard to find Replacement for the Obsolete and Discontinued original SP-368 8 Ohm 1W Speaker I found a possible RSU Part number on the net of 11936861 -info is unverified.

If you have low or distorted audio, it's quite possibly a bad speaker.

8 Ohm .5W Speaker has an OD of about 1-3/8" and .20 Thickness.  

Easy to replace only requires the removal of a few screws and to solder the two speaker wires.

Photos show one installed in my radio along with a catalog page from 2002 RS Catalog to show what this fits.   Catalog and Scanner Shown for illustration purposes ONLY and are NOT included.  Sale is for 1, speaker only.