Stainless versus aluminum
is a misleading comparison: the specific alloys and processes really matter. Some aluminum
alloys are quite corrosion-resistant while others are not. Stainless type 304 is not nearly as corrosion-resistant as 316 - which is one difference between older and newer Monitors. Personally I have seen old windvanes of both aluminum and stainless fail from corrosion
, but have also seen both hold up very well over time.
As for processes, welding to stainless tubing can be vulnerable to corrosion
unless the inside of the tubing at the weld is passivated (all SS welds should be passivated, but that can be overlooked on the inside of tubing, and it can be harder to detect corrosion).
The "stainless is better than aluminum" argument is just too simplistic.
BTW the mixture of SS fastenings with aluminum parts
is a different issue: heavy corrosion is a result of large differences in galvanic potentials. Those should be protected with LanoCote or something more high-tech.