I've spent considerable time going through the minutiae of the report. There are the usual lessons for the maintainers and managers as a temporary repair became "permanent".
Pilots doing walkarounds and finding old tailstrike repair doublers on pressurised structures may want to have a look at the pictures on page 185 of the report (perhaps somebody could host these photos). Description follows:
2.2.5 RAP Preparation Data Collection during 6C Check
In November 2001, CAL performed a structure patch survey to collect the data for B-18255 RAP, and the following photo was taken as shown in Figures 2.2-5.
The photograph was taken from underneath the aircraft looking up towards the fuselage. This area of the aircraft belly slopes upward towards the rear of the aircraft. When the aircraft is parked, the forward end of the doubler is closer tothe ground then the aft end. There were several traces observed on the doublers and the skin around STA 2100. Traces 1, 2,and 3 are brown in color and straight toward the aft of the aircraft, suggesting that the traces were induced by the relative wind during flight. Trace 4 shows several curved lines of transparent condensate liquid that flowed from STA 2090 toward the forward (lower) end of the doubler, consistent with flow due to gravity when the aircraft was parked. The traces seen in the November 2001 photographs were not evident on the wreckage when it was recovered.
Traces 2 and 4 began at the same origin but went in different directions. It suggests that trace 2 occurred as the aircraft was in the air, but trace 4 occurred when the aircraft was on the ground. The darkness of the traces shows the accumulated time and quantity of the flow. The color of trace 2 is the darker, which suggests a larger quantity of flow escaped into the air stream in flight.
This phenomenon, discovered during the accident investigation upon examination of photographs of the 1980 repair doubler, showed that there was possibility hidden skin damage beneath the doubler in the vicinity of STA 2100, at the time when the photographs were taken.