Yeah you have more chance of that happening with the DFIs when out of warrenty compared to the old tech engines when both have been maintained well but I think the opti has now been more or less fixed, they were a real time bomb years ago early 21st century but the problems got more or less ironed out due as usual to a very willing cohort of guineapigs to test on their time and dime, still not up to the expectation the 4strokes seem to have or the older carb and efi engines but better regardless. Once upon a time if an engine had a problem before 600 hours it was a dog, today it seems if the engine is trouble free for 200hours it considered reliable.
You situation is a bugger, to save 10k I would get it all new myself mainly because of the engine warrenty, the waiting time will be the decider I bet!
Be sure to get the entire history of the engine from mercury before paying paying a dime also a full workover including compression, if it will be the selling dealer who does the compression, be there to see the guage at each cylinder.
good luck
cheers fnq