( which is a brand new one for £45 from Auto Dr)
Would that be from AutoDoc.co.uk ?
I notice Autodoc offer a variety of non-OEM, as well as 'remanufactured' £100+ calipers from Bosch, Ferodo, Budweg etc.
Do you recall what brand of caliper you purchased?
I came across this video showing how to refurb Honda rear calipers
https://youtu.be/KqrOyDlbLvIA bit more complex than simpler front calipers.
I fitted new Bremetch (Brakes International) front calipers after failing miserably 3 times to order a set of Pagid remanufactured calipers from carparts4less due to problems with their website. Also fitted new Pagid discs and pads without too much trouble a few months ago. Only minor issue was with shims not fitting Pagid pads properly.
Still undecided what to about the rear calipers in long term. Factory original rear brake parts are working fine despite age, so no hurry to change anything for the moment.