It sits below the banjo fitting. If you look inside of the lower fitting, you will see how the ball fits and seats on the internal surface. It is machined to the curvature of the chrome check ball.
'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, 8:41 R&P