If you have any leaks on your guttering then it is either a blocked guttering, down pipe or the joint has failed.
When cleaning out the guttering, the gutters should be wiped clean inside to allow the water to flow correctly. The down pipe should be tested with a bucket of water to check that the pipe is clear. Two buckets maximum should tell you if the down pipe is blocked.
If the gutter joint (Union) is leaking. Replace the part! Do o allow it to be sealed with sealer. It wont last last long, causing you to pay once again. Insist on the part being replaced.
Hope this helps