The new engine is great however, from the get go, the boat was slow despite the 25% additional HP. Much confusion ensued.
The hydraulic pump had been overhauled as part of the new installation, but not the motors as these had (theoretically) done half the work of the pump over the previous 20 years. First mistake!
Over this winter we removed them and sent them back to ARS Anglian Diesels for overhaul. They expressed surprise that the props had turned at all... Anyway, we got them back, and bunged them back in along with a brand new spindle valve control unit (cheaper than overhaul), checked direction of rotation and said "Jolly good, that's that done" Wrong...second mistake!
After launch in April we went even slower...3.5 knots (ish) Ooops. And fairly quickly the pump started making a buzzing noise, indicating cavitation. Much head scratching later... "Its the hose from the tank" says I.
Sure enough, That hose had a collapsed lining, so we changed it and the others in that loop (oil cooler, return etc). Nope, the pump still buzzed and the props hardly turned.....
So, reluctantly we removed the pump. Fortunately my (genius!!!) design of an engine raft allowed this in a few minutes without removing the engine itself....Phew.
The pump was completely fuggered (technical term for destroyed). the oil starvation had damaged the swash plate, barrel and pistons in less than 4 hours of running.
We are now waiting for the courier to return it and will be replacing the 4 hoses to the 2 motors as we put it all back together...
Lessons Learned:
1. Hoses are lifed items. On an industrial plant they last about 5 years but the conditions in a boat are generally more benign. even so these were 20 years old and had gone out of production in 2002. Don't assume that, because they look OK, the insides are in one piece.
2. The pumps and motors in these drives are high speed compact items and will wear out. At the slightest hint of reduced performance get them checked. Early intervention will save hundreds of £££ later.
3. Check your filter. any black particles is a bad sign although mine was surprisingly clean.
4. Any unusual noise, check it out...

I am a (retired) RN Weapons Artificer. Hydraulic oil runs in my veins but I still cocked this up. The system is brilliant but it still needs TLC. I have rapped my own knuckles.