As always, coming to the form with my tail between my legs praying someone here can save me again! lol very grateful for everyone thats helped me over the years solve a bunch of issues. Anyway long story short, the car has had a iffy pedal since I've bought it two years ago, seems like it has massive travel and very squishy. Maybe 25% pedal but when it engaged after the travel the car does seems to stop decently just feels sloppy and unsafe almost to the floor I would say. It first went to a local mechanic who inspected the system suggested a faulty master last year, I went ahead and purchased a used one w/ vacuum booster off of ebay on an apparent low milage part out (probably not my smartest idea buying such an important part used) he installs it, bleeds breaks, same thing squishy pedal & travel. Fast forward to this week I've been working on the car and I've done everything in my power and knowledge to figure this out to no avail. I've replaced rear calipers because they where a rusty mess and a bit seized, also new breaks and rotors in rear. Same thing upfront newer calipers and rotors all working correctly, breaks have 3/4 life left. There are no visible leaks on any of the lines, calipers, master cylinder, booster, ABS, & I am not losing fluid in the system. (Recently flushed by mechanic) I've since replaced the master cylinder again but with a rebuilt one from autozone. (Bench bled and followed instructions on install) then proceeded to bleed breaks in the correct order, no air bubbles clean fluid. Again same thing no difference in the pedal at all & and this point I'm at a total loss. My last thoughts suggested by the service manual could be a internally leaking ABS module because something weird is happening. With the car off I pump the break the pedal does firms up and does feel ALOT better, but if keep apply constant pressure it will basically sink to the ground! Signs of a bad master? But cant be I just swapped it out and its not weeping. Service manual suggests ABS assembly but no ABS light no check engine codes just a mystery BAS ESP that has also been on since I've purchased. The only thing that has not been replaced since I've started working on this is the booster (used one mechanic installed) but like I said no signs of leaks around it no rust does not seem to be weeping either! I'm going to dig around the site and see if anyone has some testing methods for it. In the mean time if anyone could give me a suggestion or where to go at this point I would greatly appreciate it!