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I was excited to see that one of the shingles comprising the inner wall of the nozzle extension was damaged. This showed the double-walled construction of the extension and the "Z bar" supports separating the two walls.

Picture 2 of 3.

Apparently, this amount of shingle damage isn't that unusual. According to page 1-125 of the F-1 Rocket Engine Operating Instructions [direct link to 324M PDF] (p. 176 of the PDF itself), "Engine Damage Limits,"

Condition	Limits
NOZZLE EXTENSION
Shingle thermal buckling	Acceptable condition
Slot locally opened or closed due to thermal buckling	Acceptable condition
Shingle axial overlap opened	Acceptable condition
Shingle overlap eroded	Remaining overlap must exceed 0.030 inch.
Shingle erosion	Up to 0.375 inch as measured across major dimension is acceptable.
Shingles pulled away from Z-bars	Up to 2 adjacent Z-bars are acceptable.

It looks like the shingle's been pulled away from three adjacent Z-bars, but even with this amount of damage, the nozzle extension is nearly flight-ready.