There is no such thing as heavy rain in the North Sea compared with the tropics. Sometimes I have been unable to avoid walls of water in China but there has been no reaction from the engines and the chip baskets would break it up anyway. I believe, but unable to confirm, that a Bristow 330J had an engine failure in heavy rain in Brunei and they replaced the the snow dams as a precaution. During my time in Belize with the 330C Puma with open intakes the biggest hazard was rain stripping off the tape on the rotor blade leading edge.