I have a 1997 BMW 740il with about 35 tho miles and since I bought it last year/May
it makes this rather annoying tapping noise. Probably a lifter. The engine takes 8 qts.
of synthetic oil which I have changed, and the filter, about 500-600 miles ago. How
much MMO can I add and for how long should I drive the car before a complete oil
and filter change ?. I do know that I will have to take out some of the oil before adding
MMO, so that I do not exceed the oil capacity requirement of the car. Many thanks.

Our normal recommendation is to replace between 10 to 25 % of your regular motor oil with Marvel Mystery Oil.  For your 1997 BMW, drain out 2 quarts of motor oil and add in 2 quarts of Marvel Mystery Oil.  Keep the Marve Mystery Oil in the crankcase until your next regularly scheduled oil change.