Water Pump problems of the 2011 Toyota Venza

I had a 2011 Toyota Venza. Notice oil leakage. Took for oil and filter change and a check. Nothing was found, however four months later car began rattling and driving rough - I took to dealership and was told the water pump needed to be replaced. I have since found out that Toyota has had a many issues with the vvt-I oil line failures and water pump failures- both that lead to a failed engine!! they fixed the water pump, however 45days later, my vehicles just stopped running as I was driving down the road. I checked oil - it was empty! car would not start. I had car towed to dealer. I was then told 3days later that I needed a new engine! that the compressors were bad. In my research I found that when the compressor is starting to go out- the vehicle begins to run rough! this is what was told to the dealership. I believe they failed to properly diagnosed my vehicle. And they wanted me to pay $9400 to repair!!!! $5500 for a used engine!! if Toyota knows they have the issue with the oil line. . . They should have checked for this. . . And checked the engine when they know that the water pump failure effects the engine!!!!!! I am not the mechanic!! the service guy at the dealership had his head down the entire time . . . He knows they screwed up!! of course taking no ownership. I asked him why wouldn't they check for engine compression when I told them it was driving rough - he says they just don't check for that!!! not my fault. . . . This is not what I expect from a Toyota- has anyone else had this issues??? vehicle had 168,000 miles. I had a Toyota landcruiser with well over 220,000 miles and never an engine issue!.