Amen to that!
Indicator stalk: Old one was intermittent and the indicators would buzz if I moved the stalk slowly. New one off ebay fell apart (and I had to modify the connector to make it fit). I took the risk and bought another from a different supplier. Fluked that! Its worked ok for over a year so far. The switch is different than the original (series one type). It feels much better - more like the series two type.
Crank angle sensor. Replaced original mid-this year. The new (ebay) one (Delphi brand) lasted a few months then went funny. It would die and shut the engine down if I revved it to around 5000RPM (in gear). It wouldn't restart until I dowsed it with water. It was a public holiday, so I couldn't get to Holden so I went to Repco. Bought one there. You guessed it: Delphi. So I waiting to get a real one. Fitted that. No more problems (yet). Radiator hoses: Had the heater tap fail at 200,000 k's. Realised then that I had never replaced any water hoses... Bought a set off Supa Cheap. Fitted them all (and a new heater tap - from Holden). Next week one of the hoses failed. Sprayed coolant all over the engine bay and windscreen! I just didn't trust the Supa Cheap ones. So I bough a set off Holden. Cheaper by a mile than the same set from Supa Cheap! And you can tell the difference. Much softer rubber, all part numbers on the hoses. That was 130,000k's ago. No more problems.
Alternator: Yes, I bought a new ebay one. Now a year later its whining.
By all means go to ebay. But check the price from a good Holden dealer first (the prices DO vary from dealer to dealer! My wife's Cruze blew the water manifold - very common on these!. Guy at Repco said he doesn't stock them. Go gto Holden. I rand one dealer (in Canberra) quoted $145.
Rang another dealer (Canberra) closer to home, where I usually get my Commodore parts. $95. Still VERY expensive for a piece of plastic but still cheaper then another dealer.