I have a stainless impeller on my sled (115 hp Yamaha) and still have the original unused NEW aluminum one that I would sell at a reasonable price. I am not sure if it would fit the merc 90, but many of the lower jet units are the same for many outboards.
Send me an E-mail if this is an option for you. I am sure that you could call a dealer and find out if the impeller would fit and get a ballpark figure for a new one there.
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C/R > A good thing > fish all day,into the night! Steve Ng

Dad, think that if I practice hard, they'll let me participate in the SRC ?
[Gig Harbor Puget Sound Anglers....Join your local chapter. CCA member