My two cents....spend the money to have trans diagnosed at dealer or by your dad. Find a good used trans from a reputable salvage yard (there are quite a few) if that is the problem. Make sure they will stand behind it for 6 months at least, most will. The V12 can be a money pit but it sounds like you bought it right. Search for good salvage parts when needed since BMW thinks quite highly of their genuine parts (expensive). Find a dealer who sells under list price for the oem parts you need....check Ebay, there are a number of authorized dealers who do. Use the genuine BMW brand oil sold at the dealer 5W-30 full synthetic. It is a good oil and cheaper than mobil one by far. Use a genuine oil filter, it's worth the extra few bucks. The recommended oil change interval is 15000 miles. I would do it every 7500 since you have some miles on it. Check bimmerpost.com as there are quite a few knowledgeable and helpful people on their....just be careful as there are also a number of dumbasses. The E38 7 series is one of the best BMW's ever built. Have fun.
