I replaced the plugs on my 740TI and noticed that there was one (cyl 4) that had oily threads. Is this a leaky piston ring? I read somewhere that a spoon full of ATF through the spark plug hole into the cylinder can seal up a worn piston ring. Is this true and should I use dino or synth ATF?

There are a lot of reasons. You'd be looking for the business end to be fouled, not the threads.

Like clifford screamed, it is often from a valve cover gasket or cam seal/distributor seal dribble. Or because someone perhaps oiled the threads when they put the plugs back. Antiseize it and forget it. I doubt you're looking at any problems.

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Chris Herbst, in Wisconsin.

NO DONT ADD ATF TO YOUR CYL HEAD.ATF HAS A HIGH DETERGENT ADDITIVE THAT CAN LOOSEN THE OIL RING SEAL.IN MOST CASES OILY PLUG THREADS(NO. 4 CYL)IS THE CAUSE OF A LEAKING CAM COVER GASKET!