Which one?
I’ve no experience of Rose warranty dept- and generally that’s where your contract / warranty would lie if they were UK based, but all of the leaky Shimano calipers I had fail were replaced instantly with the latest generation (via Merlin – although slowly).
#Edit: Anyway I have no idea of Rose actually send them back to Shimano, or if you’ve put olive oil in there, or anything else, but I think your question really should be about Rose.
And lastly I’m not being critical or anything. I’ve got Reverbs from Germany that SRAM have honoured the warranty for – via UK shops with no quibbles. But you and I are both pushing the distributer boundary / envelope a bit and sometimes I guess it wont work out.