.When I look into the threaded receptacle for an injector I see a 3/8" (or so) hole in the sloped bottom of the receptacle but no heat shield.

Robert
From what you describe above it would seem to me that you had no seals in when you removed your injectors. The seal seats on a 20º cone with a 10mm Dia hole as you describe. My guess is that you are assembled correctly with one seal. You would surely have had problems with leaks using 2 seals.

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Beagle