Don't scare the man! Of course do not hose it down with your pressure washer or hose pointed right on it, but don't be afraid of it either. I have changed at least 20 of these things over the years and I have even gotten pretty good and rebuilding them.
I have seen people drive through a car wash that had the under car rinse and have the car stall. Give it a few hours, go back, hit the key and all is good with the world. These units are not air tight, and with the constant hot and cold cycles they do get moisture inside. Just be careful and you will be fine!!
Also you can change these out in about an hour, on the vet you dint even have to remove the shroud!