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It seems the brass/Tufnol interface cannot survive long term without some lubrication. Though I found no trace present when purchased secondhand. I emailed Casella about lubrication but received no reply. Presumably these instruments are now obsolete and no staff remain who have any knowledge of their maintenance. I shall try oiling the wormwheel to see if that helps. Re-polishing the brass/bronze worm may also be necessary. I'm waiting for a still day before I start trying to lower the supporting pipe.
A further update: Having taken down the anemometer and removed the lower plate the fiber wormwheel was dark but lightly polished. The brass/bronze[?] worm looked rather dull. I applied some Castrol LMP grease to the worm and re-erected the anemometer on its pipe. Only for it to start groaning and whistling again! Obviously not due to a lack of lubrication on the worm. So, back down it came and I removed the cup rotor to apply a few light oil drops to the top and bottom ball bearing races. When it went up again it remained completely silent and spun far more freely. It is now reacting to light gusts far more quickly and slowing more slowly.
Click on any image for an enlargement.
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