[THIN] OT: partially uninstalled component (MSI based)

I have a small app that installs with an MSI and all the files got
uninstalled somehow, but the registry things it's there, and it keeps
trying to fix itself.  I can't remove it using add/remove programs.

I can't re-install it because it's set to require an uninstall before it
can be installed again. I have the product id, but where exactly can I
rip info out of the registry/file system so it will let me install it
again?

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