I don't know what is causing the sponginess. The car will stop fine but it is not as firm as I would like. I redid the bleeding from Right rear, left rear, right front, and left front and it is the same feel. So I suspect is it the master cylinder. Is there any way to fix it by keeping bleeding the brake lines or I have to remove the master cylinder and do a bench bleed again?

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.