Definetly buy the new pod. I wouldn't fit parts off ebay especially an rcbo or any other safety device. Not worth the small saving.
Yet again, you get conflicting advice, Willrose electrical actually selling some used RCBO/pods on EBay.I have use dEbay seconds as a last resort and sometimes you just have to go down the seconds route if the client doesn't want a whole new board
I have also sold over 500 used Rcbos , Rccbs , Elcbs , Rcds and Mcbs on Ebay so the market for seconds is very strong indeed so lots of sparks are clearly fitting them an alot of them
Most pods are type A even old ones they are more common than AC.Are the new pods Type A RCD?