I agree that you should consult with an attorney right away. Although it appears that the work was just done in Thanksgiving of 2011 (though in your post you wrote 2010), the statutes of limitation always run more quickly than you think, and the more quickly you address this the better the evidence will be. Many attorneys offer free or low cost 30-60 minute consultations, and if you take any paperwork that you have from the first mechanic to the consultation meeting, you and the attorney should be able to come up with a game plan by the end of that meeting.
If you haven't done so already, you should be sure to get pictures of the "not genuine" parts that were installed. And, if the attorney you consult with believes that there is a possible cause of action against the mechanic, he/she is likely to want to work with you to get at least one solid statement/affidavit from the mechanics at the Peterbilt Dealership that makes clear the "defective, not genuine" parts were what they found when they took your semi engine apart, and that those parts are what caused the damaged you've suffered.
All the best to you!
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Based on the facts you describe, you seem to have a cause of action for breach of contract/warranty. Every legal action has time limits, so you should immediately consult your own attorney to protect your legal rights.
Yes, assuming you had the work done 2 months ago, you have a pretty good cause for breach of contract, and possibly also fraud as well as unfair business practices.
It should not be difficult to prove that the parts were not genuine Cummins parts, and that those parts were what caused the damaged you have sustained.
Based upon the significant amount of damages, you ought to hire an attorney to bring a lawsuit on your behalf.
The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author (who is only admitted to practice law in the State of California). For specific advice about your particular situation, consult your own attorney.
If you think that the auto shop deliberately used defective or less-than-agreed-upon parts, you may want to consider a complaint to California's Bureau of Automotive Repair. BAR has broad investigative power. Where BAR finds it appropriate after an investigation, it has the power to shut the business down and order restitution and other very severe financial remedies. Most reputable auto shops will go to substantial efforts to stay off of BAR's investigative radar. Sometimes a customer's demand letter that a BAR complaint will be made is sufficient to cause substantial efforts by the auto shop to resolve the dispute.
My responses to questions on Avvo are never intended as legal advice and must not be relied upon as legal advice. I give legal advice only in the course of an attorney-client relationship. Exchange of information through Avvo's Questions forum does not establish an attorney-client relationship with me. That relationship is established only by individual consultation and execution of a written agreement for legal services.