1.New engine replacement is the way to go.
2.There are plenty other engines other than Volvo to choose from.
3.You will find another make of engine. (Many of them better than Volvo). ( I have discovered their boat engines do not match their car engines). Do not be worried about an engine not fitting in exactly. You will have to change engine mountings etc but these adjustments are not a major problem if you find an experienced fitter. Generally i think modern engines are smaller than older ones.
4. You should consider finding a fitter first and take their experienced advice on the replacement.
5.I would be happy to consider a professionally reconditioned Yanmar if I found one.
6. Do not expect your existing prop shaft and propellor to be suitable for your next purchase. The propellor must suit the engine /horse power as lack of performance under engine often comes down to this and people fail to see it.
7. It is also your chance to have an indirect cooled engine with the added advantages this brings for hot water and inboard heating if you want to sail in cooler months.
Best of Luck
Billy
The membership association for owners of Dufour Yachts