Both front and rear deore m615 brake callipers appear to be leaking oil onto my brake pads and loosing pressure, I have bled multiple times and changed pads, they work for a couple of rides and then stop working quite quickly.

Can they be repaired? Or should I just replace the callipers (though cant seem to find any online currently)? Or is this a known problem with the brakes and would I be better just getting some slx’s or other brake (would need to be budget)?

They can be repaired, but it sounds a bit faffy – replacement is cheap and easy – is guess most calipers will fit – Deore ones tend to screw in, higher spec ones use banjo connections so check before you buy if you don’t want to change the hose.

2 year warranty on those . Send them back if they are not that old .

Yes it’s a know problem with those brakes, and I’m never entirely trusting of other level shimano callipers either. The seals develop a micro leak when they get a bit old or dry and as they can’t be replaced it’s a calliper swap required. The leak is small enough to have no impact on the feel of the lever, but the discs wail, don’t stop, and have an oily deposit in them. Irritating as it is I still run Deores because they’re so relatively cheap, and replace callipers every couple of years.

Nothing you can do really. My rear went after 4 yrs without any obvious leaks but just squeal and loss of power. . £25 or something for a new calliper. Bargain.