If I can source the bearing, and it is not too expensive on its own, I wouldn't mind trying replacing it. It could be a shot to nothing - given the price of the whole replacement pump (about £450!). Hopefully I may be able to find someone would have the relevant bearing press to remove the old bearing and insert the new one, unless the appropriate tool is readily available and cheap (probably not). I do have a couple of torque wrenches for assembly.