B&G Masthead Unit
My anemometer stopped turning and after rescuing it from the top of the mast, I decided to replace the bearings. That didn't work out so well, because the lower housing (part no. 213-10-038 in the exploded view found in the Photos section if you search for "Masthead Unit") was frozen onto the the threads from the part above it. I tried everything to loosen it, but in the end it twisted off the threads from the part above, so now it's not repairable.
I'm writing only to note that there was an o-ring above part 213-10-038 to seal it to part 213-10-003 (it's not shown on the view noted above). The o-ring was hard and stiff. If it had been replaced at regular intervals (5 years?) it would have saved the $1,000 cost of the new one.
If you do try to replace it, I would not torque it very much at all. The threads coming from the part 213-10-003 are pretty delicate. I believe it's salt crystals that caused the threads to sieze.
In contrast part 213-30-008 unscrewed easily from 213-10-003, probably because water running downward did not tend to collect there as it did in the lower part.