Diesel Engine problems of the 2013 GMC Terrain

We bought a 2013 GMC Terrain in April 2018 with 129k miles for approximately $15k after tax and title. We had it for about 8 months and were bringing it to a local Chevrolet dealership for routine oil changes every 5,000 miles. About 1000 miles before our next oil change in December 2018, we noticed the engine knocking. The dash illuminated the check engine symbol. We connected an obdii reader to the pcm at a nearby part store. The reader displayed the code p0014; which is relative to "camshaft position 'b' timing over-advanced or system performance bank 1". We discovered the code was associated with low engine oil. We checked the oil level and there was no oil on the dip stick. We needed to poor 3 1/4 quarts of oil into the engine. We needed to add approximately 1 quart of oil every 1 1/2 to 2 weeks thereafter. About a month went by, and in January 2019, the dash displayed an engine power loss message and the engine sounded like that of a diesel engine. When the engine was shut off, we noticed the oil had leaked all over the ground. The vehicle was brought to a mechanic who diagnosed it as having a rear main oil seal failure, piston rings were bad, and the timing chain was bad. We called the dealer where it was purchased. They noted the vehicle was no longer under warranty because it has over 135k miles on it and they were unable to compensate for the damage. We called the gm customer service headquarters directly, and they informed us the vehicle was not listed as having any issues or recalls according to the VIN. $3500 estimate to fix by private mechanic. Vehicle is currently being serviced.