Have had this on a couple of motors and is quite dangerous as it can lead to brake failure,the last one was on a Vauxhall which was caused by a build up of corrosion on the wheel cyl alloy itself,pushing one end away from the back plate with the shoe only resting on the very edge of the piston,the other on a Renault which may be more relevant to your vehicle,it was a couple of years ago and renewed both rear wheel cylinders, if I remember there were issues fitting the new ones, they were sitting with a gap on one side between the backplate resulting in again the piston sitting very close to the edge of the piston,can't remember if they were a two or one bolt fixing but resolved it by clamping a small split pin on one side of the cylinder between it and the backplate which straightened it out and looked much better when sitting on the shoes. I made sure they were the correct cylinders from the supplier and not had any bother with it since then. If your shoes have been saturated the I would definitely renew them along with the cylinders themselves,making sure the are contacting the shoes correctly, don't take chances with brakes, good luck.
cdc
April 2016
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.