This helped for me. The foam packing material in the cover, back corners were rubbibg on the zipper making it difficult to go around the back corner. I trimmed this away and that helped make the zip travel smooth. Rubbing the zipper with candle wax helped as well. The zipper tends to fix itself if it doesn't get banged up too bad.
YES this is a good fix to prevent the zipper from binding
I trimmed off foam around the 2 front corners on the upper lid and then rubbed a bar of soap on the zipper all the way around and now it works great
i still need to be careful going around the front corners but it works a lot better
my first case zipper broke and i found a new case on ebay for 30.00 $ and yes i bought it