1 rear calipers do jam on just change them
2 replace rear brake lines and do the front to rear ones at the same time you’ll need new lines if they haven’t been done already as the corrode wherever they are clipped together and round the rear subframe I did my own with pipe from the auto store as I had my own brake pipe nipple former tool and I did the driver side rear In 2 pieces with a joiner union
3 if you snap a brake bleed screw off the front caliper don’t panic buy a larger bleed screw from an auto parts store normally they sell a 3/8NF20 screw so you drill out the original In situ without removing the calliper and then run the tap in ( bottoming tap ) and fit the new one it’s a simple job with new sharp drill bits and will save 100s on a second hand or new caliper
4 if your brake lights start to stay on this will trugger errors for ABS HDC and rear handbrake module I didnt fit a new switch as I thought I’d try a little trick -I glued a small flat plate to the pedal sensor plate to reduce the size of the gap between the reed switch and this did the trick
5 do bleed the vehicle thoroughly as per FFRR posts Then drive it and brake hard on loose to get the abs working on all 4 wheels then bleed again and if necessary again but only the standard DIY bleeding not a full bleed process with the GAp tool this isn’t necessary - until you get a hard firm pedal the brakes shouldn’t be at all spongy
6 brake boosters do go bad there is a spigot inside which is retained by a collar these can “pop” under sudden forceful braking - master cylinders don’t seem to go bad although I did replace mine
7 you will need to remove the abs unit to change the booster I used a gap IID to re bleed the brakes from scratch and it uses at least 5 litres of new fluid if not more if you follow the gap instructions After all this I realised how bad my brakes had gradually got over time they are now awesome 🙌👌

Great info thanks for posting. My brake pedal has always been quite spongy even after several good pressure bleeds. I have a GAPiiD tool but according to support, my 2005 4.4 V8 Petrol L322 does not have the option to bleed via ABS pump. I replaced the master cylinder and had to crack each pipe at the top of the ABS unit while pressurising the master cylinder to bleed the ABS unit then bleed the 4 corners. The gravel braking thing is a great idea that I haven't tried so that is on my list to try next. My pedal is very solid with engine off but has always been spongy with engine running. I upgraded to 4 pot Brembo callipers a few years ago so it stops well but the pedal has always bothered me a little. My most recent issue was heavy noise and vibration at low speeds <20MPH that shook the car and sounded like a truck stopping. This was right after fitting new front Brembo pads to used but good EBC disks. Eventually I ran the Stop-tech brake pad bed-in process which amounts to 60mph firm braking to 10mph without stopping then repeat 8 or 9 times in succession to heat the disks and pads and get material transfer from pad to disk. Disks will be pale blue if done correctly. This seems to have done the trick but time will tell. I have also found that I can access both rear calliper bleed nipples from under the car on high suspension setting without jacking or removing the wheels. Saves a lot of time and effort.
Hopefully this info will add to your original post and help someone else too. I'll update when I've tried the gravel braking and re-bleed thing.

PAYNTS wrote:

...brake boosters do go bad there is a spigot inside which is retained by a collar these can “pop” under sudden forceful braking - master cylinders don’t seem to go bad although I did replace mine
7 you will need to remove the abs unit to change the booster I used a gap IID to re bleed the brakes from scratch and it uses at least 5 litres of new fluid if not more if you follow the gap instructions After all this I realised how bad my brakes had gradually got over time they are now awesome 🙌👌