2003 TJ tailgate hinge screws not budging

Well...that makes sense. I remember years ago, an old Italian guy, retired Fiat engineer, told me why many older European cars had rubber plugs on the rockers and fenders. They were supposed to be opened once a year and sprayed with something like used motor oil to protect the under carriage of the car against corrosion. And I read about many folks up north here in the US and Canada pretty much doing the same to protect their cars against salt and harsh winter conditions.
So I guess I'll start doing something like that on this Jeep.
Thanks for the advise!