Windows Media Player 12 volume levelling

I use Windows Media Player for my music digitised from vinyl and generally find the volume levelling helps, but was wondering if I could adjust the value for a few files that it doesn't have right to my ears.
I read that WMP uses PEAKVALUE and AVERAGEVALUE tags for this. However, if I display these in Mp3tag and insert a value, it makes no difference. I tried putting in a field and value for REPLAYGAIN_TRACK_GAIN and this does change the replay level, but only once! Changing it again has no further effect, and you have to remove all tags to get rid of the effect you created.
This suggests to me that WMP stores its replay gain information somewhere else. Does anyone know where, and whether I can effectively adjust level in Mp3tag for WMP playback?

Sounds to me like a WMP update problem.
To update data in WMP you either wait until WMP has scanned through the watched folders or

  • delete the updated file(s)
  • select Extras>Restore deleted items

and see if the updated data is now effective.
It could be that WMP also stores this data in its database - which has a proprietary format which cannot be edited. AFAIK.