Porsche 924 924s 944 torque tube bell housing inspection cap 477 521 277 C ((CB53))
This is the rubber cover that fits at the rear of your torque tube to allow access to undo the rear prop coupling. Fits pretty much all the 924 and 944 range. Part number is 477521277C. It keeps the muck and road dirt out of the gearbox bell housing.
Photo for reference purposes only.