2011 Jeep Grand Cherokee V6

So I went to two separate shops last year as my brakes were acting strange (the pedal would take a minute to release, and on incline stops, I would roll back and have to go into neutral to stop). I ended up replacing the master cylinder, and it didn’t fix it. I took it to another shop. They couldn’t figure it out. Took it to another shop this morning. They said whoever bled the brakes after the master cylinder replacement or whoever looked at it after put in motor oil and not brake fluid so the entire system is toast. New everything they said besides lines if there was a way to flush them out with brake cleaner. ABS module, master cylinder, calipers, seals, rubber hoses, etc.

He said it’d be 4-5k, all said and done. Has anyone heard of this before? I can’t sue anyone as I don’t know who would be at fault here. I know my way around a car and have all the tools, but I don’t have a lift, and it’s too long to fit into my garage. Not sure I would even know how to tackle the more sensitive areas like the ABS module beyond replacing it. They said it’s extremely dangerous to drive it.

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Thoughts?