i would be looking at the calipers if your brakes are spongey , mine were spongey for ages and no amount of bleeding , replacing master cylinders etc would fix it, i then noticed when i was under the car that the calipers could move around freely and i worked out that when i took my foot off the brake pedal that the piston in the caliper would also retract too far leaving a small gap between the piston and brake pad , do this on 4 wheels and there is your spongey brakes,
i ended up grinding / cleaning off the rubber backing from the brake pads so they had nice clean metal on the back face only , doing 1 wheel at a time i removed the pads and pumped the pedal once to bring the piston out further , put the pads back in and only pushed the piston back in enough so i could just slide the caliper over the brakes , did this to all 4 wheels and now my brakes are like new with maybe 10 mm of pedal movement before pulling up the car where before the pedal was traveling 80 plus mm before the brakes started to pull up
i know this is a quick fix but it has led me to realise that the rubber seal in the piston is at fault and seems to be flexing rather than sliding, and yes i have recently put new kits through the brake calipers in the process to finding out why i had spongey brakes which only fixed it short term