Technical Spare O ring

[digger58]

Hello all,
Just finished putting my x engine together after a full rebuild, 1989 GF, I see a spare O ring and wondering if there should be an o ring in one of the water galleries between head and block? any ideas? see photo. Hope I don't have to strip it again.

 

[Tiffx19]

I don't remember an O ring there- that looks like the O ring for the distributor shaft maybe?

 

[digger58]

I don't remember an O ring there either but the old one definitely has residue similar to the water galleries on it. The one in the gasket set is a different size to the old one as well. Can't figuer out where the old one came from then again there were several botched jobs on the car when I bought it considering there were only 9500 mls on it I'm not surprised if it had spurious bits and pieces, there was PTFE tape on the sump plug!