How much rust is too much

Working on some trunk rust issues on the Cuda. Got the whole floor and extensions out. Wheel wells can be patched. Question I have is on the tail panel. The bottom section is rough. There is some good metal under the rust, but back side around the taillight brackets is bad too. I hate to replace the whole panel, since 90 percent is good. But the bad part is what the trunk welds to. Hate to put time money and new metal to leave rust that reforms and destroys my work.

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How much rust is too much
Author: Martin