PART NO.  SPL.PAGE  DESCRIPTION                                                           
AAA4657   16.R.46   Washer  -(for union at pump return, heater, 1600 and 1600-MK-II) -was
    300398

AAA4657 Copper sealing washer (crush type). For heater return water spigot to 3-way pipe in coolant near water pump inlet, MGA 1600. Part number was 300398 for 1500 model.

Alternate numbers:
Moss USA number 324-660 :
Moss UK number 232043A