Extreme temperatures and leaking guttering joints.

[Ken Durchgang]

The guttering joints on the southwest corner of my house (and my mother's next door) which get the full heat and direct sun of extreme heatwaves have been leaking far more often and worse than any other part of the house ever has. I'm guessing that current plastic joints were designed in an age of lower summer temperatures and hence less expansion. Any one any ideas of making plastic guttering joints cope with higher more extreme temperatures and extra expansion or any new joint products that will do this? Thanks.