To be honest it would be way more worth it for you to buy a decently low millage used engine from bavauto.com they are an excellent resource and have been around for quite some time. We have used them several times for used bmw engines and so far everyone one of them have been perfect. If you had like an old M5, M6, M3 or something where a used motor would be hard to find or very expensive I could see a rebuild being worth it. But the 740il are very easy to come by and usually under 2k. Good luck if you need any help please feel free to contact me at my shop at 813-949-3540 or 703-314-6511. Good luck!