[Shell500]

Hello,
In the last few days, something strange happend to my brakes MT200. Sometimes when I push the lever it's weak and it almost touches the grip. Sometimes it has no problem and works ok and sometimes it's in the middle. I can't understand why, the bike has 1 year(and has a lot of problems even tho is new:madman but I've never done nothing to the brakes. I found out that was a little o'ring from the caliper that was about to fall off. I took it out and it was oily and now it doesn't stay in its place. What is that o'ring? I had this problem since I installed new brake pads(I've never pressed the lever with the rotor off)

 

[Lone Rager]

That's just a rubber cover over the bleed port. It's only there to keep dirt/dust out. If fluid is leaking there, you need to tighten the bleed port screw. In the top pic, you can see that screw to the right of and perpendicular to the cover. 1/16 - 1/8 turn should be plenty to stop the leak. It just needs to be firm, not crazy tight.

That said, since it's been leaking and your lever is going to the bar, the brakes will need a bleed anyway.