Job done! & mower returned to service.
Even though its a Hydro-Gear transmission, it was cheaper to purchase Ferris/B&S OM fan.
New 25HP engine, full service front to back - so far going very well. Transmission a real pain in the rear to refill - took best part of two days to percolate in.
As just coming out of our winter, true test will start in few weeks, as grass starts to grow.