MARVEL COMICS - TRANSFORMERS, Technical Question?

I have a complete set of Transformers (Original 1984, etc...) comics issues 1-80. I've always been interested in how much they are worth and I didn't realize there have been reprints of these comics and some are worth considerably less than others. As I have just sorted through them I can tell some differences between issues because I have 2-3 copies of most of the issues. My biggest problem is figuring it how to tell which is a first print and which is a 2nd print. Any help?