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Hi all newbie to this site ,having brake issues on my 2019 2litre diesel insignia ,rear left is binding ,disks are dirty telling something is up ? Auto park break sounds OK, any ideas

Hi i am new to this forum so be gentle with me , my car is a 2019 insignia sri 2.0 l the problem is the rear left brake seems to bind ,disk is bit rusty ,which tells me something is wrong put new pads in ,but gets very hot and is binding ,any clues to fix this.?