In previous times, there were quite a few Buhk conversions to Yanmars. My 31 footer had a 3 cylinder Buhk and was converted (before my time) to a Yanmar 3GMD/20. Fitted well, slightly less weight. Not everything is as easy to access though.

Checkout a Yanmar 1GM10, still available new, and some pop up every now and then second hand. The Yanmars come with sail drives, but probably doesn't fit to the Bukh unit.
www.yanmar.com/marine/product/engines/1gm10/

What are the symptoms of the propulsion problem?

Hi Brisa
Re: On the first two occasions the boat had no thrust on forward but it had some thrust in reverse. However, on the third incident the boat was very slow and after about 20 mm we lost all thrust going forward or in reverse. We have spoken to a gearbox specialist and he says it sounds like the spline on the sail drive is the problem.


I don't want to confuse the matter, just want to help you come to a good decision.
I am not a gearbox specialist by any means but I have trouble with the idea that it is a damaged spline.

What brand and model is your saildrive?
What have you dug up on the net about other people dealing with this problem?

we suspect we may need to replace the engine and sail drive.
Why would you need to replace the engine when the problem is in the gearbox?

We are waiting for Bukh to come and check the boat again
By that comment it would seem that the Bukh people have been out and looked the problem before.
What did they say about it?


We changed the bushings and have replaced the propeller but the problem has reoccurred
Who recommended replacing the propeller?
What bushings are we talking about here?

You will have to be on the hard to do any work on the saildrive, so I would be looking at a second hand or reconditioned replacement.
Then you could have the original reconditioned and sell it on to try to recoup some of your outlay.

Gary

The yanmar ones are frightfully expensive.

Hi keensailor.
Would that be a Bukh engine coupled to a yanmar saildrive?


gary

Howdy
A mate of mine has a small Volvo motor attached to his NS27 saildrive.
Another option maybe