To follow up on this, I spent countless hours bleeding my brakes to no avail. I replaced all the rubber hoses that connect to the calipers (they were showing cracks anyway), I replaced the master cylinder, and I followed the BMW bleed procedure to a "T" several times. If anything, I made it worse. I also observed some weird phenomenons with just getting endless bubbles. More searching forums revealed others who have fought this issue to no avail. A couple people mentioned they had success by wrapping their bleeders with teflon tape. Since one of the weird things that was happening was... after shutting the bleeder, bubbles would continue to flow through the clear hose attached to the bleeder nipple, I considered this. That was a head scratcher that indicated air was somehow getting in the line even with the bleeder shut.

I had little hope, but back up on jackstands she went today. All the wheels removed AGAIN. I started by removing each bleeder nipple and carefully wrapping about 3" of teflon tape around each. I then reinstalled the nipples and ran the BMW bleed procedure as I had before. I have a homemade pressure bleeder, and I ran the bleed procedure in ISTA+ for each wheel separately with the bleeder open. I didn't seem to get many, if any, bubbles out of the rear brakes, but the RF brake had a lot of bubbles. I ran the ISTA procedure a couple of times with 5 brake pedal full pumps following each time. Eventually the bubbles stopped, and I moved on to the LF where I got fewer, but still significant bubbles. I then shut the bleeder and put my foot to the pedal and GLORY BE!!!! we had a firm pedal!

Ultimately, the problem was all caused by air leaking around the threads of the bleeders. Intuitively, I seriously doubted that could be my issue, but I was proven wrong for the second time in a decade (sorry, corny dad joke). This problem was really grating on me, as it just shouldn't be this hard to bleed a brake system and get a firm pedal. Anyone need a perfectly good, used master cylinder? ;-)

AM.

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E70 2010 3.0 M57 AT Titanium Silver with Black Leather
E53 2004 3.0 M54 AT Toledo Blue with Gray Leather
E83 2008 3.0 N52 AT Silver Gray Metallic with Black Vinyl
E46 1999 2.8 M52TU 5MT Black with Tan Leather 250K+ miles (Sold, but not forgotten)