You misunderstood what you heard, or heard such a misunderstanding retold. The propellants were indeed corrosive, but the engines were built out of 6A1-4V titanium alloy which had been tested to surpass mission requirements including strength, heat tolerance and corrosion resistance. read more
You'll see that Apollo 13 had a very similar entry time to the other missions. You'll notice two standouts - Apollo 11 and Apollo 15. Apollo 11 has a longer entry time because its profile was shallowed a little so that it would land a bit further downstream, to avoid bad weather. read more
Note: To celebrate the 40th anniversary of the Apollo 13 mission, for 13 days, Universe Today will feature “13 Things That Saved Apollo 13,” discussing different turning points of the mission with NASA engineer Jerry Woodfill. read more