Hello from Oz...
Not relevant regarding the oil leak, but O have had some experience with after market vs OEM parts.
Engine is an Ecotec V6. Had a crankshaft position sensor fail at about 300,000 klms. Straight foward. I bought an "ebay" item, fitted it, problem fixed.. So I thought.
The replacement dies after about 5 months' service. I couldn't get to the dealers to buy the right one (long weekend and I needed the car), so I bought a supposed OEM one from a local parts supplier. When I got it home and opened the sealed box (no returns once the box seal is broken) it was the same brand as the "ebay" one!.. Needless to say, I had to fir it. All good. Car was back on the road. For a while. This sensor couldn't cope with anything over 4,000 rpm. At the point it would shut the engine down. Only way to get it to restart was to shut it down, and restart. So... I then paid twice as much and bought the real OEM one. Same brand as the original. All good now. Revs to rev limitter, and it has lasted 3 months. Spot the lesson!
At about 200,000 klms, and probably 13 years, one of the radiator hoses started leaking. As it was the first cooling system problem the car had had, I decided to buy a complete set of hoses. Went to the local parts store and bought the set. Duly fitted and away I went. The next day I was driving on work business and one of the new heater hoses split! About 2 inches long split! Limped home and asap went to the dealer. Bought a complete set of hoses. Cheaper than the local parts store! That was 6 years ago. No more leaks and no more failed hoses.
Stick to OEM. And make sure if you are getting your own mechanic to replace parts, that they use OEM parts.
