After searching for an alternative to pricey Oberdorfer seals for my N202M-16, I was able to obtain equivalent seals that are easy to install ( no tools needed) and are made out of the same rubber material with the same expected life of 2 to 3 years in salt water, My experience has been that only the seals need to be replaced more often than the carbon bearing or the impeller. I replaced them 20 hours ago with a groove on the shaft and there has been no leaks so far.
Visit my website Alternate Seals  for more information and view the album.
You can order them from Grainger. You can also contact me if you would like me to order them. If there is enough interest we may be able to get a discounted price for a larger order which I will ship them to you. I would recommend ordering 4 to start with.Since they are small and light weight, they can be shipped USPS for a bout $6.00, I will have to confirm the price. Please note that its is at your own risk.

Grainger
Seal 61CK17  $ 14.87, it is unclear if this double lip seal is suitable for marine use since it is made of MBR and its garter spring is not stainless material. Its dimensions match the requirement.
Currently I am testing the single lip version of the above lip seal Grainger part number 61AA52 $12.88. With 20 hours of engine time there is no water leaks.