For bleeding the pressure bleeder is really nice. I use the wheel pins to hang the bottle from, once the wheels are off can probably do all 4 corners in less than 10 min. I'd be dreading reaching up and working on the pedal area much more. My metal brake pipes have a fair bit of corrosion, I worry about them and need to replace them. If I had what you have I would be really checking them, under the plastic covers etc as I know they are suspect. If yours are for sure ok I agree it is probably master cylinder.

https://www.amazon.com/Motive-Produc.../dp/B0002KM5L0

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'05 E53 3.0 6mt
'17 F30 340ix 6mt
'96 E36 328is, in progress