Holden Statesman Engine Problems

YOURS is not the only car that has failed to respond to the fix. Others have been rebuilt more than once. I would recommend you reject the area manager's assessment and pursue a fix, probably another rebuild. I would doubt that the rattle will get any worse and it's unlikely to cause any major problem in the long term, but it sure will be an annoyance now that you hear it. I wouldn't be so concerned about the rattle, but I would be careful about high oil consumption. I would certainly get it fixed.

THE V8 Adventra was a bit of a dog in many respects, but 20 litres/100km is a bit too high. The Adventra is a heavy old nail so I would expect it to be pretty thirsty. I would think it should get 16-17 litres/100km on average. The only thing you can do is to make sure all is well with the engine and the electronics controlling it, make sure your tyres are inflated correctly and that wheel alignment is correct.

IT'S impossible to be sure without listening to the noise you complain about but it does sound like the piston rattle that afflicts many Gen III V8s. Some 5.7-litre engine Gen III V8s suffered from piston rattle, some from high oil consumption, some from both. Holden's fix is to fit new, tighter, Teflon-coated pistons. I would persist with the dealer until you get a satisfactory resolution. On the face of it, you have cause for complaint.