As do I, frankly I don't understand how the bolt length makes it leak but this is the prevailing theory..
I'ts quite high up, around head gasket level I'd say, the top idler pulley bearing has copped it (squeaking heaps) and the compressor is soaked in oily residue. Both sides have residue, but there's none at head-level (doesn't appear like a rocker cover leak) and there's little to none towards the rear of the engine. Car has done 250,000 km's so probably never been cleaned. I guess if it leaks again it will likely be a small, slow leak like it is now and likely not a critical issue so I can just keep an eye on it and where it's leaking from precisely.