trust me I have been there and done that...........................sorry but get a new engine from BMW or scrap the car.......I hate to say it but, I had the situation with my X5 4.6is ,I had to cut my losses after a bad oil change . I had to wreck the 4.6is and I bought a 4.8is with low miles , she is a bit of work but I am happy now.....................all the best.
DON;T TRUST ANY ONE TO WORK ON THE X5 ..................make sure they are certified