I have tried putting a couple of 'keepers' either side of the Nd magnet, which do reduce its strength sufficiently for the reed to open and close properly, but the additional weight of the 'keepers' is such that the bucket tips too early and completely upsets the calibration of the gauge.
I have looked for a traditional Alnico rod magnet of the right size, but cannot find one. Plenty much bigger, and plenty of Nd magnets of the correct size, but nothing in Alnico.
It seems my only solution is to remagnetise the old rod magnet. I have tried heating it to dull red heat and then picking it up with a little Eclipse horseshoe magnet while it was still hot, expecting it to retain some magnetism as it cooled, but it didn't work. I don't understand why not; I thought that was a standard method for magnetising steel.
I'm open to suggestions as to other methods for remagnetising the magnet, bearing in mind it is fairly small.