Well you are not likely to hear much good about Volvo engines on this forum. It would appear to be an overall consensus that parts are hard or impossible to get in North America, are overpriced and further that Volvo does not support older models. I however have a 1981 TMD40A with low hours and from my understanding from the previous owner of more than 20 years the engine has had only minor issues and standard parts, filters, belts, impellers etc. are readily available. We were fortunate enough to acquire a multitude of engine parts with the boat that had come from a hurricane Sandy boat which was salvaged. Look forward to other opinions.
My experience is not like that quoted above.
My boat was built in Taiwan, the standard Ford Lehman was rejected by the original owner and the Volvo TMD40s were substituted as an upgrade. Those were 145 hp engines. When I bought the boat they had 3000 hours. I put another 1500 hours on them without incident.
At that time, my Volvo mechanic talked me into buying a pair of TAMD41s rated at 200 hp that Volvo had taken in trade on an upgrade for someone else. These had only 1500 hrs on them at that time, so I sold the TMD40s for almost what I got the newer engines for. Had that deal not been so good for me I would still have the 40s,
In my view the cost of parts is not an issue, as these engines are rarely in need of anything more than the usual preventive maintenance items. In the 1500 hrs I had those engines, I put new Heat Exchanger boots on both, which I was able to get easily and inexpensively. Other items I had to buy were belts, hoses, filters and fluids. All readily available and reasonably priced.
I know several boaters who have had serious work done on a variety of engines, CAT, DD, Cummins, and they all have stories of the high cost of parts for their engines.
It will all be considered high when it is unexpected.