I looked at a 2004 boat this week with twin Volvo Penta 5.7 GXi, V-Drive, 400 hours, salt water use. May 2019 (when the current owner purchased the boat) the boat had all risers/manifolds replaced because water ingestion was found on one side of the port engine. I reviewed the details/documentation from the mechanic, copied below, and it looks like all the right steps were taken to address the underlying issue. Should I be concerned about future issues from this repair? Should the heads have been rebuilt as well? Should I be concerned with this comment "original seal had left a groove in the prop shaft." Boat was sea trialed and surveyed after this work and did very well. My offer would be contingent on survey, sea trial, engine compression checks and oil samples. The boat was winterized in December, oil was changed then so I would not expect much negative back on an oil sample. ISSUE "Performed visual inspection of engine, found rust buildup around exhaust manifolds and components below indicating water leak/gasket failure between exhaust riser and manifold. Motor mounts rusted. Noted sea water pump rubber vibration dampener deteriorated. Noted some serpentine belt wear present, recommend regular inspection of condition. Performed visual inspection of fluid levels and conditions. Engine oil full, appears in normal/good condition with no evidence of water or metallic contamination. Transmission fluid appears in normal/good condition with no evidence of water or metallic contamination. Noted distributor cap and ignition wires appear new. Noted water in bilge under port engine, prop shaft seal dripping water. Previous service records provided by seller, did not review. Removed and inspected spark plugs, found rust staining on several spark plug electrodes, evidence of water ingestion on engine. Several plugs found wet with water. Performed cylinder compression test, after testing four of eight cylinders engine started pumping water out of cylinders, unable to test wet cylinders. CYL 1 - 155 PSI, CYL 2 - 130 PSI, CYL 3 - 250 PSI, CYL 4 - 190 PSI. Tested cylinders very inconsistent. Removed outboard side exhaust manifold from engine to isolate cooling system and prevent further water intrusion to engine, attempted to purge cylinder of water and finish compression test. Noted cylinder head exhaust ports, outer valve faces, valve guides and valve stems rusted. Rotated engine by hand and found valve stems notrusted in movement range area where valve stem seals would be comprimised. Visually inspected cylinder condition as much as possible with borescope camera, found evidence of light rust staining on cylinder walls, no visible pitting or scoring. Recommend immediate replacement of exhaust manifolds and risers. Recommend spark plug replacement." SERVICE/REPAIRS Met with customer to discuss findings from engine surveys. Covered work surfaces in boat with 4,320.00 protective mat where possible. Removed cockpit seats, removed floor panels from boat. Continued troubleshooting water intrusion into port engine, determined cooling passages in exhaust manifolds and/or risers breached. Removed manifolds and risers from port engine, two manifold bolts broke. Cranked engine to purge all water from cylinders. Performed compression test on remaining cylinders. Inspected exhaust ports and valve stems, found ports and stems rusted. Slowly rotated engine over and found rust on valve stems only existed in exposed areas outside of valve guides. Met with customer and discussed findings, customer elected to continue with exhaust manifold repalcement and see how engines ran after repairs. Coated cylinders and exhaust ports with fogging oil to protect from further rust during service. Moved acetylene torches to boat and set up, heated and extracted remaining pieces of exhaust manifold bolts. Scraped and polished cylinder head surfaces, checked with straight edge to verify sufficient gasket sealing area around exhaust ports. Installed new Volvo exhaust manifolds, risers, associated gaskets and asteners. Installed new spark plugs in all cylinders. Test ran port engine at dock, engine started easily and appeared to run well. Rechecked fastener torque, rechecked hose clamps. Removed and replaced starboard engine exhaust manifolds and risers. Cleaned and surfaced conditioned cylinder head surfaces, checked with straight edge before installation. Replaced all spark plugs. Started and test ran engine at dock, engine ran properly. Sea trialed boat and confirmed engines performeing properly, no abnormal noise, vibration, power loss, etc. noted at this time. Noted water leaking from port prop shaft seal. Moved boat for haul out. Removed port prop for access to slide shaft back from transmission, removed shaft zincs and bottom paint from shaft. Removed coupler bolts, found coupler seized to shaft. Made and installed coupler puller, removed seized coupler from shaft. Removed and replaced shaft seal, adjusted cutlass to place shaft seal in a different position on the shaft , original seal had left a groove in the prop shaft. Reinstalled coupler and prop shaft. Replaced shaft zincs and repainted prop shaft. Reprimed all water intake strainers. Launched boat and test ran engines, checked shaft seals and found no leaks. Boatwas run by salesman for 1+ hours at high speed. Removed and insepcted spark plugs, found no signs of water ingestion or damage. Performed second compression tests, all cylinders came up to Volvo spec range. Reinstalled spark plugs. Reinstalled floor panels, seats, etc. that were removed for access. During service one battery repeatedly went dead, recharged multiple times, multiple times needed to use parallel switch to jump start engine. Battery failed load test. Replaced battery. Cleaned boad and made ready for delivery.