I’ve got a Saint calliper that is showing signs of a leaky piston seal (loss of power, squeaky etc). I’ve seen on Shimano’s website that there is a 2 year warranty – they’re 18 months so covered there – the thing is I’ve swapped the hoses over.. Will they be funny about the return because I’ve done a hose swap?

Possibly, if you’ve not used genuine Shimano mineral oil.