Will try VBRfix as soon as I get it downloaded. Excuse my ignorance but does resetting the metadata also fix headers ?

No. The VBR headers are part of the MP3 file itself. The metadata is part of the car player's internal database. Two separate things.

There is a chance that we're looking at drive/cable troubles and the source files have nothing to do with it. Not sure. Can you make it happen on the same source file every time?