recovering a corrupted git repo

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I have not had any issue until I ran a git fsck recently, which repored gzip and crc errors in some pack files. git fsck does not seem to repair the errors, only report them. I would like to try to rebuild my repository, without downloading any more from the origin than I have to. All of the commits I have added seem to still be intact, so I assume the corruption in somewhere in the upstream history packs.

How can I correct the errors, and fetch the corrupted upstream history, while preserving my patches? So far I have exported my patches as bundles, and made a fresh clone from upstream, then pulled the bundles back in, but there must be a better way that only fetches the corrupted bits from upstream?

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