so, the mechanic has mentioned that the bottom one is the most likely cause of the issue.
(mind you havent towed it there yet, booking for timing belt is Thursday)
he called it the "Harmonic Balancer". He ordered one in at just under $500aud, ordering direct from the dealer would have been closer to the $700aud mark.
sounds like my issue is exactly what pete had, and now after seeing some pics, i understand what you guys meant about the outer and inner bonding.
this fixed idler is also called the harmonic balancer?