1998 Cadillac Seville STS

I recently purchased a 1998 cadillac seville STS and several days ago the DIC read "service stability control system" and the ABS and traction lights came on. I took the car to a local mechanic and they told me that they found 2 codes that both went back to a pump for the ABS system and that that was likely the cause of my problem. But they also told me that they could not access the actual stability control module in the computer system and they did not know why. I was also informed that the repair costs would be relatively expensive and this is frustrating to me as I just purchsed the car three weeks ago. The ride of the car has not been affected and the brakes are still working fine (though I am not sure if the ABS is working) the only obvious indication of a problem is the indicator lights being on. The original owner of the car assured me that there were no known problems with the car and this might be the case though I have to wonder as there were several red flags when I purchased the car but I decided to trust the guy anyways. Could he have known? I do not know. My questions to you are do you have any experience with this problem and is there anything I can do to defray the costs of repair (I have some experience with vehicle repair and am not afraid to get my hands dirty). I spent the morning online looking for parts diagrams in an attempt to locate the faulty ABS pump but was unable to find any diagrams at all. Any help or advice you could offer me would be much appreciated