Bondo doesn't fail in any three years, even when I use it.  Of course,
I used it on a truck body, but it's in pretty good shape ten years later.

I can't imagine how either the bond or the structure in the player action
stack would have failed.  Bondo is pretty foolproof, as is evidenced by
the large population of fools who continue to use it, including me.

All I can think of is that the mix was somehow contaminated.  I wonder
if there was something on the wood -- say, some synthetic glue that had
been used previously -- that dissolved into the Bondo before it cured.

I'll bet a body shop guy could answer the question, though.  Here's all
I was able to get from a Camaro restorers' discussion group:

  "The biggest failure of "Bog" (as we call [Bondo] in this neck of the
   wood) is contamination underneath and moisture. ...

  Contamination underneath is flaking surface paint, metal surface
  exposed too long and molecular surface rust, flux, and poor clean up
  after welding. ...

  Moisture... Bog is usually an isophalic resin with a heap of talc
  and other powders mixed in, these powders are hygroscopic (absorb
  moisture), so should not be left exposed..."

Mark Kinsler
Lancaster, Ohio, USA
http://www.mkinsler.com/