Hi guys, I have had both issues - Water leaking onto the top of the sump and a leak just behind the left front wheel close to the water bottle. The water on the top of the sump turned out to be a shot water pump which is very common. This cost $75.00 from a local parts shop and took me about an hour to change and was really easy to change out. I have the instructions somewhere, if you need them I can post them.
After changing the water pump I flushed the cooling system and refilled with Nulon red coolant, then had a leak just behind the left front wheel close to the water bottle. I couldn't work out where it was comming from, just dripping off the bottom left side of the radiator and onto the plastic deflector that is attached the the bottom of the front cross member. It was really annoying me as every time I would check the water level from the cap on the engine it was always low. Apparently when the system has a leak the water doesn't get sucked back in from the overflow bottle, but can suck air from where the leak is instead. This was happening to mine as the overflow bottle was always full.
There was also a minor leak above the water pump on the pipe that comes off the engine where the cap is. There is an o-ring on the pipe that can leak.
I was ready to change the radiator and fix the o-ring. There are VZ radiators on e-bay for $102 - 2 year warranty.
NEW Holden VZ Commodore Alloytec V6 Aluminium Radiator (eBay item 230573527860 end time 13-May-11 20:13:43 AEST) : Cars, Bikes, Boats
I ended up just putting some Bars Leak in though and this fixed the problems (it won't fix a shot water pump). I have been driving it for about 5 months now with no sign of any more water leaks (only a little bit of white powerdy residue where the coolant has dried where it had been leaking and then stopped). Apparently Holden use some kind of pellets that can take up any minor leaks in the cooling system (this is what bars leak does too as it has pellets in it as well). I'd say that when I flushed the system I flushed away anything that was previously preventing minor leaks. 05_vz_ss, the last service at the dealers did they flush the radiator, perhaps this is the same thing that happened to mine?
Anyways, this has been my experience that may help you guys. It doesn't need to cost an arm and a leg to fix these kind of problems.
Good Luck!
