EA81 crank without the little rear flat O ring

[steptoe]

In my hurry to supply another block and crank to my machine shop I mixed up me cranks and was surprised to hear the crank was fine (180,00km on last rebuild ended up with stuffed main bearing and bearing housing causing vibration)

I thought it looked different but did not pick it until fitting the flywheel, there is no recess to fit the flat orange O ring. Consulting the gregories indicates some did not have this O ring. I reckon it must have been an improvement made with the 84 models onwards and suspect mine came from a pre 84 block with no water plug at the front. Filled it with silastic to be on the safe side !

Anyone know about these ??