Engine Oil Leaking problems of the 2004 Nissan Quest

I was driving with my son and the transmission line snapped. I was scared because I didn't know what happened. Thank god my son who is disabled was not in the car. My mechanic said that this should not happen. When I got my car back my transmission is now very sick. I have always maintained all fluid changes at the correct time. My car is not the same. Now today my oil pan was "eaten" from the transmission fluid leaking. I have had many issues with my Quest. This car was not built with proper parts. I can't drive it but I have to keep it for my son is in a wheelchair and is severly disabled.

I have a 2004 Nissan Quest s. In November 2007 I called the dealership to complain that every time I start my van it blows out white smoke. I had about 58,000 miles. I bought the van used from a Nissan dealership. I was never informed that the warranty was extended to 60,000 miles. The mechanics advised me to put in some no smoke/ no leak into the oil and I should be fine. So, because these are professionals, I listen. The problem persisted so I called Nissan consumer affairs department. They advised me to take it to the dealership to be diagnosed. I now had 61,000 miles. I took in my van and they kept it all day. They called to say they needed every receipt of oil changes, to prove I kept up the maintenance. They said I have a sludged motor and need a new engine. Nissan will not help me because there is no record of me calling before my warranty was up and they said it was lack of maintenance, not covered. Even though I gave a years worth of oil change receipts. Also, they never actually ran a diagnosis test on my van. They just used their expertise, and experience to come up with a sludged motor. Later my van starts vibrating quite badly when brakes are applied, so I take it to a mechanic who says I have a misfire, and a blown head gasket. (they also say this could have caused the sludged motor). I replace the spark plug 250. 00 later. I call Nissan again and say what I have been old only to be told it still would not be covered, that I need a new engine. That it isn't their responsibility to make sure the van was kept up before I bought it. I feel that if I buy a certified preowned vehicle I should not have to worry about putting in a new engine. They said if I didn't like their service I should contact the bbb. I feel this is unethical, and poor customer service. They will not help with anything and meanwhile, I am still making payment on this van. They quoted me 5,000. 00 foe a used motor and it would only have a 90 day warranty.