I managed to get the zipper back and to work ok again.............but looked about a way to lube it up a bit to ensure it works ok going forwards.
I posted my quandy on Nutz and got suggestion of Candlewax, rubbing an olde candle along the zip to keep it lubricated.
Another suggestion was olive oil - so I aksed the missus thats into her herbal stuff and she sorted me with a little bottle and a dip applicator.

I applied olive oil along my zipper inside and outside and worked it into the zip by opening and closing the zip - it works lovely now!
Worth doing!

O.