Having problems bleeding xt’s, first problem was getting any fluid in to nipple then undone the little free travel screw which helped. But having trouble with pistons, seem to bite on the yellow block ok but soon as wheel goes in no bite at all. Brakes are about 2 years old and rode in very muddy conditions, could pistons be the problem they move a bit but can’t get them to move much. Any ideas?

Blown lever seals? See if you can hear a squelchy sound when pulling the levers

My lever seals on two bikes have all blown around the two year mark, so you’re in the right territory for that. Also, one of the problems I had was resistance to fluid at the caliper when bleeding. Lever seals would be my first bet.

Worth trying to repair or bin and have some nice new ones?

You can’t get spare seals for shimanos without going to the efforts of sourcing them individually yourself.

TBH, the levers are 24.99 ea on CRC at the moment. Get a whole new lever for the cheap fix, or use it as an excuse to buy new and shiny complete. There are pretty good prices on whole 785 brakes at the moment, what with them being an out going model.

Thanks, new ones going to be ordered.