im not sure about cars being the same. but i work with marine engines and gears. hyd equipment on boats too. i purchased an engine trans from a sunk boat. was a diesel tho. i draind all fluids and opened all cylinders. put clean diesel fuel in the crank case( about a half gallon more than what you would put in for oil) thats to clean sludge and such also makes the excess water flush out faster. put about a full cup of wd 40 in the cylinders. let that sit for about 6 hours. and did the same for the reduction gear. than after it all had sit. drained the fuel out of both componets see if the engine would " bar over" to make sure it was not siezed two full rotations. then pulled the pan to inspect crank bearings. and cyl walls. they were all fine. hooked up starter and rolled over engine till all the wd 40 was cleared from the cyl. hooked every thing all up. added clean oil. and see if it would start. thing ran like a beauty. re adj. valves and sold it two weeks later. its been two years since and its never had any issues.
but that engine wasnt under water more than two days.