Two of my R21EC's had the Yanmar; the present one has the Volvo. I did the maintenance work on the first Yanmar: adjust valves, align the shaft, change oil, change filters,etc.. Never had call to do any work on the second Yanmar. My Volvo has 42 hours, I drained the oil on Monday, couldn't get the oil filter loose by hand. Will take my trusty oil filter wrench and change the filter today. Can see no difference in those tasks for the different engines. The one thing I didn't/don't like on the Volvo is the setup on the fresh water supply line. The Yanmar setup had an easily accessible fitting installed just past the fresh water filter and below the pump where one could attach a hose and flush the system; or pump antifreeze thru it (a one person operation). The Volvo system is more complicated. One has to tap in (after finding an appropriate fitting) past the fresh water filter; and there's only a short hose with not enough space to install a fitting (and it would be ackward to attach a water hose.). So, the best solution is to mount the filter higher and use a longer hose. I believe SGIDAVE did that when he replaced the engine/battery bulkhead. I'm not sure I can do the remounting on my standard engine/battery bulkhead (lack of space?). Meanwhile, my wife has helped me run antifreeze thru the system via the fresh water filter. I pour antifreeze into the filter housing; and she manages the engine controls and monitors the output thru the exhaust.
I believe the primary fuel filter will be more difficult to change. It's mounted lower on the bulkhead and closer to the hull. I know that has nothing to do with the different engines.
I didn't compare individual component prices, however I paid approx. the same for my usual order of spares. I bought my order for my 2009 boat from Marc at Wefings. Purchased the order for the Volvo at Ranger. I think one can compare those prices on the Ranger site.
I will say; I found it easier to get engine info via the internet from Yanmar. I have had no luck at all with Volvo.
I've owned both Yanmar and Volvo in other boats, a sailboat and a trawler. Both did the job. I preferred the Yanmar in the trawler, but it's an apples vs oranges comparsion.
In the R21EC, my present Volvo is quieter and runs smoother. Both engines are likely to run more hours, without major maintenance, than one of us will put on them.
Sorry, I'm late responding. Had a visit to my pain mgt. Dr. yesterday and sometimes those drugs he injects into my spinal area take a few hours of my conscious wareness away. Then, I crash.