Using steel inserts for aluminum wheels is a recipe for disaster - or more specifically, galvanic corrosion. Both steel and aluminum are anodic metals (as opposed to noble -- or how corrosive they are in seawater) and are best isolated by plastic or brass (something, anything) whether your building buildings, boats or cars, especially in exterior applications. Over time, the alloys in the metals react to one another (spurred on by salts), ionizing the aluminum and creating a corrosion layer. I'm guessing the aluminum failure in the Octavos is the galvanic stress of the new corrosion layer having nowhere to go but outward.
Short story: don't use steel (or some kinds of stainless) and aluminum together without something in between. Here's a handy chart:
Galvanic Corrosion Information
* The Galvanic Corrosion table is a measure of how dissimilar metals will react in sea water.
* Generally, the further apart items are on the table the greater the galvanic corrosion that will result.
* The material closest to the anodic end will corrode more rapidly.
Noble (Least Corrosive)
Platinum
Gold
Graphite
Silver
Stainless steel, type 316 (passive)
Stainless steel, type 304 (passive)
Titanium
Stainless steel, type 410 (passive)
7Ni-33Cu alloy
75Ni-16Cr-7Fe alloy (passive)
Nickel (passive)
Silver solder
M-Bronze
G-Bronze
70-30 cupro-nickel
Silicon bronze
Copper
Red brass
Aluminum bronze
Admiralty brass
Yellow brass
76Ni-16Cr-7Fe alloy (active)
Nickel (active)
Naval brass
Manganese bronze
Muntz metal
Tin
Lead
Stainless steel, type 316 (active)
Stainless steel, type 304 (active)
Stainless steel, type 410 (active)
Cast iron
Mild steel
Aluminum 2017, 2024, 2117
Cadmium
Alclad
Aluminum 1100, 3003, 3004, 5052, 6063
Galvanized steel
Zinc
Magnesium alloys
Magnesium
Anodic (Most Corrosive)