1992 OMC 3L Overheating

I have owned my 1992 OMC 3L (GM) for about 7 years. I started having overheating problems last year. I believe only minor work had been done on the cooling system by previous owners. I started the process by replacing the raw water impeller and the thermostat. This repair got me through the end of last years boating season. When testing the engine this spring, overheating problem returned. I started a full checkout of the cooling system. I removed the raw water impeller and checked its condition. I drained and re-flushed the system with fresh water and checked for blockage. I removed the old circulating pump and installed a new circulating pump. I replaced the raw water impeller with a new one. I launched the boat for an in-water test. Still overheating. I performed the Raw Water Flow Test as described in the SELOC repair manual (p 11-4). There was no raw water flow to the thermostat housing ... zero flow. The next step solved the problem. In the upper stern drive section, Behind the raw water impeller (after removing the plate and gasket) lies the adapter housing. This is a cast aluminum plate that can only be removed with vice grips and a lot of work. Two bolts hold it in place and, in my case, a lot of corrosion. The adapter housing is fitted with 2 "O" rings, a gasket and a Water Pump Adapter Seal. I replaced these items and reassembled the stern drive. Back to the lake for another in-water test. That did the trick. I subsequently learned that ware on these seals causes air to be drawn into the raw water impeller preventing the suction needed to draw water up through the water inlet. NOTE: The gear lub oil reservoir lies behind the adapter housing. By removing the adapter housing plate, some of the gear oil will seep out. As a precaution, either drain the level of the reservoir a bit or drain completely and refill when job is complete.