Was it hard to start the engine this Spring before you sold the boat?
How much will it cost to get reconditioned or cleaned injectors? If you search the web, there are some articles on how they are removed (you only have two, thank goodness) -- then I think you either get them traded-out by reconditioned ones or wait for them to be reconditioned.
You can decide how much cost you'd share with the Buyer. Did he do anything to you in the purchase to "work you over"?
If you were in the Buyer's position, what would you reasonably expect?
Mirror, mirror on the wall...