I no longer go through even shallow water in a car. Many years ago (OK, 1970), Elisabeth and I went through a flooded section of road on our way back to Ceduna after our honeymoon.
When we got to Ceduna, I went back to riding my motorbike and didn't drive the car again for many weeks. When I di, I immediately asked Elisabeth "How long has the diff been screaming?"
She said "What noise?"
I pulled the drain plug but no oil came out. It was a Salisbury on the Viva so I too the rear cover plate off and still no oil came out - and for a good reason, it was like a thick paste. Water and EP90 don't work well together.
That diff was stuffed. The Holden dealer charged an absolute fortune to strip it and rebuild it but it continued to whine (I was only earning about $4500 per annum in those days - including shift penalties and OT).
There were no extended breathers on the Viva diff so it sucked in a gutful of water.

