Pete, I have seen the seahorses regularly at "Seahorse Rock" for over a year now. I first saw them in January last year. I think the only time I haven't seen them was when I missed "Seahorse Rock". Last weekend I was there is 5 other divers. They swam the wrong side of "Seahorse Rock" and missed them (I did manage to attract one of them over for a look but he left me while I was taking photos). I then went looking for more along the boulders at the sand line and managed to find one more further north.
Interestingly, they managed to find a seadragon or two.
The Leap is my second favourite site (Shiprock my favourite). The Leap almost always has cool stuff (giant and reaper cuttlefish, octopus, anglers, seahorse, seadragons, etc.) but at Shiprock I almost always find something I have never seen before, in addition to the usual cool and interesting stuff.