The number of car problems solved by 'running thicker conventional oil' is limited to those where the problem was caused by running 'thinner synthetic oil'. The BMW M62 engine in the 740iL wants whatever synthetic engine oil was specified in the manual. It's always tempting as someone facing repair bills to believe in the magic of packing vaseline or banana peels into the engine instead of 'thin oil', but oil leaks are caused by degraded seals, sealing surfaces and whatever is holding tension between them. Any professional (or amateur) who suggests a smoking issue can be solved by different oil should not be trusted, listened to have business conducted with.
I watched a guy who says he is a genius mechanic on Youtube. pick up a 64 Impala Convertible using a two post lift with the arm lifting points under the rocker panels. I kept waiting for either the car to break in half, or the entire frame assembly to separate itself from the sheet metal body, which had rusted floors. He said on the video that the car was "a unibody".