I'm not sure off the top of my head which chapter and verse this comes from, but one thing in the KJV that bothered me is the verse which states that 'there are three in heaven that bear witness, the spirit, the water and the blood'. . . . and then it is added 'these three are the Father, the Son and the Holy Ghost'. I beleive that last part was added by the translator. I think that is in error.
And although the septuigent is a wonderful thing, there are most definitly many words that do not translate literally from one language to another, so a side by side comparison of many translations probably makes the most sense imho.
dc