I dont even know where midas came from or why someone mentioned it.

But can someone let me know, if a bad o-ring will cause the pedal to go to the floor.I bought from roverguy, its possible they sold me a good unit, then it just failed a week later, concidering it was great for a week

 

Yes, a bad o-ring would allow pressure to escape an your pedal to go all the way to the floor. There is always a chance of a part failing after a short time. I used to work at CarQuest and had numerous occasions where parts were returned because they failed after a short time. Happens more often with reconditioned or refurbished parts than brand new but it does happen to brand new also. I had a brand new GM starter installed on one of my GM trucks and the thing blew p after 2 weeks. Dealer had to replace the starter and the flywheel the starter took out.

Someone translated Muffler Man (which I assume is a muffler shop chain in MI) as Midas.

 

What did the Muffler shop say about a bad O-ring? If they still insist the master cylinder is bad change it out with another one. Oh, and it's always a good idea to change o-rings, seals and gaskets when installing new parts. I would imagine doubly so when brake fluid is involved. O-rings tend to swellor shrink when exposed to different environments, causing them to fit incorrectly. I would think the shop could tell if that hadbeen the problem though.

 

The shop didnt say anything about it, roverguy.com asked me if i replaced it. and i have not, and was curiuos if that could bet he problem. all the shop said, is i have a bad master cylinder again. I may bring it to another shop and tell him the story and ask him to look at the ring. i know nothing about this topic sadly, i do love to drive the LR though i can't find a o-ring by its self though from AB, i found a rebuild kit, but nothing for just a ring.

 

You may have to wait and call AB on Mon.
www.roversnorth.com has a very intesive web page, if it is on a LR they have a pic of it, and sell it too.

 

Ive ordered rebuilt brake parts opened the box in the store and found issues in the casting like stripped threads on a caliper... I just put it in the box and pushed it back and asked the guy to get me another one and waited another 3-5 days..

Plenty of bad apples make it past their quality control..