in the engine Room you find the oil reservoir for the C-drive on the forward looking side . if this looks like Bayleys Liquer your sealing of the C-Drive is broken.
Then get rid of all the oil inside, unmount the prop. replace the whole sealing kit from amel. refill the oil (8 liters) and thats it.
before refilling the oil i would clean the inside of the c-drive b y filling it with another 3 liters while turning the shaft sometimes and letting this 3 liters go out again.