The shop is responsible for that problem, if they don't want to pay for it, never let them work on your car again. If they can't get it right after 2 tries, likely they never will. My first guess would be that the rings were fitted wrong, or something like that. Did it leak out, or burn off? Its possible they didn't have enough in there or the wrong stuff, but the most likely cause is they made a mistake with the machining or assembly. 3000 miles is fine for an interval after the break-in period. How did you drive it during the break-in? Also, after a fresh rebuild, for the first 1000 miles its best to be really anal about checking the oil, like every time it cools down, you can never check it too much. There are endless possibilities for the cause here, but aside from you beating it right away (not likely) or faulty parts, its gonna be the shops fault, either in using the worng parts, doing a poor job assembling it, or bad machining. There is no way you should be paying for this, and if they try to make you, aside from never going there again, get a lawyer and sue them.