If you are in Canada, buy from a farm equipment shop. Farm equipment gets a 30% subsidy from the government ... much cheaper than a "marine" diesel shop. Some of the better outfits can rebuild them.
If you are in the US and don't want to take a chance on ebay stuff try Transatlantic Diesel
for new and rebuilt equipment ... they specialize in Perkins, are super people to deal with and they talk our language.