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A couple weeks ago I noticed that the brakes (BR-M8000) on this bike were quite spongy and since I didn't know when there last bled was, I decided to service them. Everything worked fine for about a week but then the brakes started to make noises and I noticed that both callipers were leaking oil out of the bleeding port.

I ordered some new brake pads, cleaned up everything and rebled the system and made sure all ports were closed properly. Everything looked fine until I took a first test ride. The oil again started flowing out of the bleed ports on both callipers. When pushing the brake leavers hard you could even see more oil coming out of the bleed port.

What could have lead to this issue, especially it appearing twice? And what can I do now, is there any hope of repairing or do I need some new callipers?

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    I’d entirely remove the bleed nipples to inspect the rubber O-ring and the sealing surface in there.
    – MaplePanda
    Commented Jul 10, 2022 at 21:26
  • 2
    Did you bleed with DOT brake fluid or mineral oil? The wrong fluid would contaminate the brake system.
    – mattnz
    Commented Jul 10, 2022 at 21:50
  • @MaplePanda The rubber O-rings looked fine, but they can't be causing the problem anyway. The sealing surface on the bottom of the bleeding nipple has some scratch marks but they aren't very big. Although I'm not sure how that happened, because I never removed the nipples.
    – user11914177
    Commented Jul 11, 2022 at 11:44
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    @mattnz yes I did use mineral oil
    – user11914177
    Commented Jul 12, 2022 at 7:48

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