I would doubt the oil is "bad", or, more correctly, I doubt it is the source of your problem. Check with your quench oil supplier to see if they will analyze a sample to be sure. It is good practice to have oil samples regularly analyzed and most quench oil suppliers will provide this service at no charge.
As racookpe1978 has mentioned, a little more investigation into the problem can lead to a solution. If only 10-15 out of 2000 are out-of-tolerance, that is better than 99% good, which indicates that the process is capable, you just need to adjust the process controls to eliminate the source of the out-of-tolerance condition. With a better understand of the process (batch or continuous) and your current controls, the internet may be able to help, but a carful review of the process by someone who is close to it (yourself, perhaps) will likely be more productive.
As I said, I doubt the oil is "bad", but if you have doubts, you need to check it out. More likely, it is related to the issues racookpe1987 has brought up.
Good Luck,
rp