Using latest MinGW 5.1.6 installer, i get:
Extracting w32api-3.13-mingw32-dev.tar.gz
untgz::extract -d 'C:\MinGW' -z 'D:\Downloads\w32api-3.13-mingw32-dev.tar.gz'
tgz_extract: bad header checksum
Error: Failure reading from tarball.
and installer stops.
https://sourceforge.net/tracker/?func=detail&aid=2858829&group_id=2435&atid=202435
And, since it's a duplicate of a known issue, which has been closed because it is beyond our purview to resolve, there seems little point in keeping this ticket open.