Bruce,
You should have accepted the job and a couple of months later tell them that PCA analysis shown that the oil originated from Saudi Arabia and got refined in the golf of Mexico. Attach a GC-MS chromatogram with it and charge them $10,000. I would like to see the look in their faces after that

I suspect it might have been a silicone-based waterproofing treatment that was over-enthusiastically applied, but IR would discriminate. I pointed them to their insurance company. They should swallow hard and pay the claim fee, and let the insurers fix the problem.
A lot of my calls are "CSI" influenced - neighbour's garden sprays killing flowers or making people/pets sick; fuels that stop engines, make people sick; houses that make people/pets sick etc. Usually a diverse mix of paranoia and justified grievance.
CSI shows that competent analysts look, dress, and act nerdy, and can rapidly identify the entire provenence and composition of samples in no more than 10 minutes. So, the analytical cost must be less than $100, including any court time.
Lawyers, on the other hand, look, dress, and act sexy, take the analysts data, solve the problem, get the neighbour sent to jail ( if they didn't kill them in the last 10 mins ), and are worth the $10K.
I usually suggest talking to the neighbour / supplier first and, if that fails, try to suggest analytical resources ( eg regulatory labs ) that might offer much cheaper services.
Please keep having fun,
Bruce Hamilton