What parts?
I put a pair of TAMD41s into my boat, as an upgrde from TMD40s, in 2000. My TAMD41s now have 4200 hrs +- on them. Yes, I have had some repairs done, but nothing that required parts that were silly expensive.
Oil filters have been purchased from my local Bumper to Bumper store, at the same price for the pair as a single filter for my Cummins Motorhome. I haven't tried to purchase anything directly from Cummins, so I don't know if their prices are higher. I know the filters directly from Volvo cost twice as much as from B2B, but why go all the way to Vancouver for that when I have a local supplier.
As to smoke, the amount on startup is much less than the old engines. I understand is has to do with injection pressure, which is significantly higher in these 1990 era engines than in the 1970 era that they replaced. The same would be true of a comparison with 2010 era engines with much higher injection pressure.
Unless you can afford to get into boats of more recent engine designs, you will be choosing the survivors from earlier eras. The fact of that survival argues well for the engines in the boat you are looking at.
