I saw the original production of "Grease" -- loved it. It had a nasty edge with more dark characters than good. Lots of cussing and the big dance scene between the rival schools featured an overweight Latina girl as Cha Cha De Gregorio. To this day I think John Waters got the spark of an idea for "Hairspray" from the original "Grease" production.
The movie version came out with songs cut, new ones added and it sanitized the original book (which I still have in paperback). Surprisingly it became the monster hit it is to this day and I'm still stunned.
Stage revivals in the past 20 years, I hear, have combined the music from both productions and it's also been greatly "cleaned up" to make it politically correct and child friendly.
I just played Frenchy in Grease at my high school theater...
The musical is way better than the movie, at least in my opinion. You see more character relationships and quite frankly the music is better-displayed. (And I agree, Magic Changes is one of the BEST songs...however my favorite would have to be Mooning hehehe).