[Gaz64]

Certainly an odd case you have here OliveR.

I am sure the Edelbrock family would like to know about this.

I don't see this as an assembly problem.

Considering not one other member here including one FE expert (Brent Lykins) has seen this happen with this type of guide, points to a metallurgy issue, when your guide batch was made.
Or perhaps number of cold starts versus run-time at operating temp.

Gary