Below are the rules my group is using for the used vehicles. Comments, improvements and the like welcome

In reality (whatever that is) vehicles depreciate rapidly, in fact often losing 40% of their new value as soon as they are driven off the dealership forecourt. As time goes by a vehicle’s value continues to drop so that after less than 10 years a vehicle that formerly costs 20,000+ is available for mere hundreds. But in that time the vehicles has almost certainly suffered usage and has components that are worn and tired, developing little niggles that a new owner will not know about and that might strike without warning. Not only that but corrosion and stress will have weakened the physical structure of the vehicle too, gradually making it more fragile.

To represent this a character buying a vehicle can choose to purchase one that is in a used condition. (Note that a previously owned vehicle that is in as-new condition will have an as new price. Generous GM’s may give a 10% discount.) The discount as a percentage of original price and condition of the vehicle are as shown below.

...I like this system. I'll have to apply it to Hurricane Hannah's '62 F-350.

Not bad. However, I would drop the concept of Age. Age does not have a direct relationship with the condition of the car. A year old car can be in worse shape than a 10 year old car.

Niggles, which applies Grmelins specifically to the vehicule, is great. I like that.

Fragility isn't quite right. The car should suffer from overall mechanical/electronic problems, not just lose body due to rust.

Off the yop of my head, I would give a dice penalty on all Car tests with the vehicule. Harsh, but if the player chooses to buy a car at a fraction of the price, he should suffer adequately.

...I would debate adding a negative DP modifier just because a vehicle is older. Niggles (or Gremlins - whatever you want to call them) are a serious enough penalty. In Rigger 3 they used vehicle stress points Unfortunately as with most of the alternate rules in SRIII, managing vehicle stress was cumbersome. I actually would rather keep the Fragility rating. Maybe instead call it "Wear and Tear".

I could also see a character with vehicle mechanics being able to keep the vehicle running adequately through regular maintenance using the "Wear & Tear" as a threshold. Failure would mean that sometime before the next regular maintenance session something could go wrong.

Keep in mind even a new vehicle can be a lemon. (look at the Yugo, the Pinto, the DeHavilland Comet 1, the DC-10, & The Issaquah Class Super ferry)

I agree that maintenance matters more than age. I have had three year old cars die, nursed 18-year-old cars back to health and run 'em strong, and the cars I've had that were in the best shape were so old your system would write them off; over the age of 6.

The theory is nice though. I just think the execution should take treatment into account. Babying a car and doing all the maintenance on-time will make it nearly timeless. Flogging it will take it's toll but not too badly if you keep an eye on trouble-spots. Neglect will kill a car quickly.

To illustrate this point, let me tell you about my first car. It was the only one I had for over a year and that still ran when I got rid of it. I gave it to my father-in-law. He doesn't believe in maintenance. He wondered why the engine blew six months later. He NEVER changed the oil (nearly 10K miles) and I told him NEVER EVER EVER EVER run 87-octane in it but that's all he ever ran. I used that car harder than he did, but I took care of it.
The worst part is that it outlived my wife's car despite being 11 years older.