I'm taking mine out this winter .... the engine (a MD 2030) is smoking and low on power, needs a rebuild but AFAIK the saildrive is fine. I'm repowering with a new D1-30 + 130S so both the MD2030 and the ms25s will be sold for spares or reconditioning around March next year if you're interested.
Rare as hens teeth as when they fail there is usually nothing you can do - as you have probably found out. There used to be an outfit in Lancashire that attempts to recondition them, but don't have details now. Your best chance is finding somebody like Baggywrinkles who is replacing a whole unit. When mine failed you could get new ones at OE prices, although only 130s as the 120 went out in 2005 and that is what I did, but the ratio is different so needs a prop change as well. If you can afford it, this is the best solution, but at today's prices it is arguably better to fit a complete engine/drive and recoup some of the cost by selling your engine.