Land Rover Repair: 2004 Discovery engin replacement., piston slap, landrover discovery

Question
I have a 2004 landrover discovery that has always run a little rough (engine knocking) along with other drive shaft issues, and new brakes every 10-12k. The truck wiring harness also caught fire when they forgot to secure it after a service(they replaced the ECU and wiring I was told). I have always changed the oil every 3k and every time it made a noise taken it in. It had the 35.5k service on time under the warrantee and took the car in just before the warrantee expired and asked them to review the engine noise one more time to make sure it is not something that is going to cause me issues in the future. They told me the noise is piston slap and not to worry "most of the Bosch motors do it". My service advisor also told me that as long as I keep the oils changed like I am and keep the coolant full the I should not waste my money on the extended warrantee. I just paid $900 for the 60k service were they said they go through the whole truck front to back and the motor. This was about 2 months ago and the oil light came on after long drives (over 20min) when in idle. I had about 2500 miles on the oil and check it to find I am a quart short. Should not be a big deal s is hold 7 quarts. I take it in for an oil change and tell them about the light. They say no codes or faults I am good to go. The oil light came on after a long drive I call they tell me to bring it in in 2 days. I am now told they need to look a the oil pump to see if it is clogged and if it is not I am in for a 12k new engine. Do I have a leg to stand on when it comes to getting them to replace the motor on them not me?

Answer
If you have written documentation of their incorrect answers, then possibly.  If you don't have paperwork probably not.  I recommend speaking with your lawyer if you want to pursue the issue.

I've never heard of piston slap on the bosch engines, my wife's DII doesn't do it.