It was PG and even with the blood and some gore it never received an R. It wasn't until Indian Jones came out with a PG rating when parents were pissed. After that we now have PG-13. About a few years ago I bought Uncle Buck on DVD to watch with the kids. I didn't realize how much swearing is in that movie and it's also PG.
I remember when Logan's Run came out, it was rated PG and there was a lot of full frontal nudity. I remember many parents gasping in the theater and being upset by it.
Funny, here is the IMDB parental advisory for Logan's Run. I don't remember all the nudity that this describes but I do remember seeing Jenny's boobs!
A woman comes to a man's apartment for sex. She changes her mind, but before doing so her buttocks can be seen through her toga.
During the chase scene, the main characters end up in a place called "The Love Shop" where citizens of the city come for orgies. As can be expected, there is both male and female full-frontal nudity.
Later on, the characters strip during a scene in a cave. The female (Jessica 6) shows full-frontal nudity, while the male character (Logan) does not.
When the two escapees are outside they strip and skinny dip. They swim around each other and the woman's breasts are visible, and their buttocks also come into view when they dive under the water.
There is a scene in which the characters Jessica 6 and Logan 5 are shown a hallway filled with frozen humans, all of which are fully nude. Many of the women can be seen fully frontally nude, although the groin area for some is behind clouded ice, but only partial frontal male nudity is shown.