Rusted Stainless steel. HMMMMMM!!!!!

[Rexone]

Stainless alloys differ in corrosion resistance by the amount of chromium and carbon in them. Your prop is obviously on the more corrosive side of the spectrum which is not surprising because of the high strength necessary.
Try cleaning it with scotch brite (never use steel wool or any steel product for cleaning stainless alloys) or a polish with a good degree of cut like Simichrome. If kept clean it should not be a problem unless you leave it in the water for long periods of time (oxygen stravation). If the rust (oxidation) is left on it however it will deterioriate, although at a much slower rate, like any steel alloy eventually to the point of pitting and permanently damaging the metal.
Stainless alloys like 316L have a much higher degree of corrosion resistance because of the low carbon content (the L).
Also the higher polished the finish (cleaner) the more resistant most ss alloys are to corrosion. A clean piece of stainless with no contact with regular steel will self passivate over a few weeks. Passivation is a process normally done chemically which uses an acid to remove the free iron from the surface of the stainless steel and forms a very thin transparent oxide film coating.
Bottom line is keep the prop clean.
>>>Here's a pretty good link to the details of chemical passivation of stainless steel (http://www.pfonline.com/articles/119806.html)

[jkh04200]

There are many many grades of stainless and they all differ some. What rust is carbon steel. Most metals have some amount of carbon in them. In a alloy reference guide I have, in the stainless section, there are over 100 listed metals. The carbon content is what is in question here. For example 303 SS can have as much as .15% carbon where 316L has a .03% max. There is even a 319L that is .02% max. The cheaper stainlesses will rust but at, say 1/50th that carbon will. If it was a problem I'd just keep a light coat of oil on the prop. If you have some surface rustin on your prop, do not use any steel wool are a buffing wheel that is made of carbon steel. If will rust even worse. Use a wire wheel that is made of stainless. The carbon that is in the buffing wheel and or steel wool will leach into the prop and make matters worse.