I think what you can do is
1) split the video at the point where audio starts getting out of sync (I think the tool to use here is virtual dub)
2) demux (separate) the audio and video streams of the out-of-sync half using avidemux
3) open the audio file with goldwave, stretch/squeeze the audio length so that it is the same duration as the video.
4) remux the new audio file with the old demuxed video file in step 2.
5) upload the video in 2 parts, part1 being the split 1st half which is already in sync, part2 being the newly fixed, remuxed file.
This way involves no degradation of video quality. I think audio has to be transcoded in goldwave but that's about the only quality loss.
Hope this helps
You could also ask Aces, if something doesn't work out cuz he sucessfully fixed a progressively out of sync highlight file
