BP Ultimate works

[Big_Richard]

.

[TJ 450]

That's the fuel injector insulator. On the M117 and M117, the main body of the injector actually sits above the surface of the cylinder head/intake manifold and is encased in those plastic insulators. There is an O-ring at the base of these, plus the rubber seal as on the M-100 at the top, which is held in with a clamp.

The arrangement on the M100 is much more robust IMHO as there is only one seal, constantly under pressure from the clamp, so you're not missing anything.

Tim