[Oliver James]

My gutter is leaking at the join. It is one of those semi-circle shaped uPVC gutters.

Any ideas about how to go about fixing it?

[tom20001]

From my experience when gutters leak at the joint the gutter has simply moved away from joint a little so it is no longer clasped on rubber in joint fitting properly.  Simple enough to fix just adjust gutter length back ensuring it is past rubber in gutter joint fitting.

They must move in the wind or something as it seems to happen a lot

[p1w1]

As above really probably just moved of the rubber a bit probably. Guttering expands and retracts over the year with the hot and cold weather also sometimes moss can start growing between the rubber seal and plastic. I would actually just replace the joint myself (only a few quid) and half hour job taking your time.
Also the plastic clips on the joint can weaken and crack as the plastic degrades over the years.

[ray mck]

Seen it a lot lately,is your gutters black.

[ray mck]

Should say are your gutters black.

[Plankton]

Unless it like this customer who said he had a leak, https://www.facebook.com/burnbraecleaning/photos/pcb.1532037620193679/1532037576860350/?type=3