The W50 is based on a BMC block. I believe that it is 1600 cc. I was never able to find any source of parts or model number for it as it has been out of production for many years. I was told that basic rebuild kits (rings and valves) are no longer available even from Westerbeke though I was occasionally able to find parts from Torrenson and other places that had replacement stock stuff on the shelves.
I would venture that your leak at the throttle valve on the injector pump is a classic indication of a need for a rebuild of the pump. My rebuild cost about $700. Most diesel shops can do this and the injector pumps were made by just a few manufacturers for multiple engine manufacturers, but as I am sure you know-- it requires the services of a special shop set up to rebuild these. I am told that the newly formulated fuels and some additives will hasten the death of old injector pumps.
I had no option but to replace mine with a Yanmar
, but would recommend that folks attempt to keep their W50 going as long as possible. A replacement is about 10K for the engine and about that again for the labor to install and replace everything you are going to need to revise and fix to get the engine in.
Good luck.