Got to www.ct1ltd.com look up the tube of sealant ct1 then stockist list top right of page you may find one near you. The main concern is is your gutter safe to work on ie: not old metal and ready to collapse.
So is it Metal or plastic?
I will send more info if you want I'll post contact, you can reply using the answer form to your question.
Although the product above sounds a very good repair route.
Retired to Worthing from Ealing West London Where I put up and took down miles of guttering.
Bob
August 2010