Do some research with regards to bimmers with oil leaks and using stop leak. This product softens the seals and BMW engines have a lot of them. Its not a good idea and will probably cause more harm than good. This next time around that you have to change the rear main seal you are going to want to check the condition of the cap. Do you know if the rear main seal was changed as a whole system which includes the gasket, metal mounting cap with rear main seal inserted and new bolts? Some people take the cheaper route by picking out the old seal and installing the new seal. In the process of picking out the old seal sometimes they nick the journal of the cap and this causes the leak. Whats even worse is when someone nicks the crank journal and at this point the engine has to come out to fix or replace the engine. When BMW replaces the rear main seal they sell and install the whole kit that includes the integrated mounting cap with rear main seal and gasket. This way you stay away from nicking critical components when trying to replace just the seal. By yours being done twice and the same problem exists someone did not do something correctly or failed to see the cause of the real leak. But what ever you do not use stop leak. Perhaps you may want to consider selling the X and finding something a little less expensive to maintain and care for.