robG your the man.
all curiosities now sorted. Just need to go buy some now.
I take it a well bugger idler arm will make racking, clacking general unhealthy noises???
It can do, but you should notice some odd steering issues before it starts making noises. The steering box arm is on the drivers side and the idler is on the pas side. These are swapped sides at manufacture for left or right hand drive cars.
So, if the idler on the pas side fails you'll notice it in the steering. As the drivers side wheel will be held firm by the steering box, but the idler will allow play on the pas side wheel. So you'll have adjust the steering wheel to allow for the change in toe (tracking) setting caused by the idler play, and possibly feel the pas side wheel flapping around.
There should be absolutely zero vertical play in the steering idler to centre tie at the rod ball joint end of the idler. Any flex while leaning and pulling on it (use all your strength) at all and you'll get tram lining / odd steering sensations.
If its bad enough to make noises then the bush has at least partly fallen out and the metal surfaces are banging together while the idler flaps up and down.
And as said, use genuine gm only to be as sure as possible to get a part that will last. They are over £100 retail. £90 on trade though.

Its worth checking for vertical play before ordering, if not done already.

I've had a lemforder idler from All German last less than 6 months. Which is poor. Very poor.