Do i have a case against the dealership for concealed defect, bought 1999 siena

Did you get ANY kind of warranty papers , or did they sell it to you "as-is"? The paperwork they gave you is the best start. Let us know.

It is a Mandatory law (Lemon law) you have 72 hours to return any vehicle that is Financed to the dealer purchased from that starts 24 hours after you sign the contract for any reason with full refund.it does not matter weither it was advertised as is or with warrenty. SO to answer your question you do have protection from this kind of Dealer my advice is to while during your test drive go to a oil change place and get the oil changed it is best to be out of $20 bucks than $6,000 and if the salesman refuse then forget that vehicle