Hey, welcome to GTPlanet both of you!
I have to agree here. Getting golds on the early licenses will really help you out early in the game. I was always short on cash until about the end of the Beginer's League. But after that the money rolls in pretty quickly.
The cars tell you when they need an oil change. There is a light on the 'dash', in the RPM gauge. It's supposed to come on at 300 miles or so. But if you can afford it, get it after every series like coffeepot suggested.
You can also get a few extra horse power in your car if you change the oil imediately after you obtain it. This trick works for any car. It will go up a bit more after you run a few races and get the oil changed again. That's from the 'breaking in phase'. Then you will see it slowly and steadily decline (even with regular oil changes) from then on. This is just a piece of the 'realism' that they've tried to incorporate into the game.
If you're wondering about why there's no car damage, we at GTPlanet tend to think it's because the manufacturers didn't want their cars all smashed up. I don't agree with that arguement because Burnout has car damage, and it has a lot of the same cars as GT3.
~LoudMusic