"Change it! I have a 1980 800
"Change it! I have a 1980 800 and I noticed cracks in the transom seal around 10 years ago. I never got around to changing it. I thought it would be a much tougher job than it is. Last weekend the boat almost sank. Sat at the dock for an hour, then headed out and and couldn't figure out why it wouldn't plane. Then I noticed the 4 inches of water in the back of the boat. Engine was half under water but kept running. Got back to the marina and trailered it. Seal had a 2 inch slit at the bottom. I had run the trim full travel several times the week before to change the water pump belt and I guess that is when it went. Lesson learned.
You can find the seal on ebay and I ordered a service manual CD on ebay also. I got my old one off removing only the trim fin. Prop stayed on. Remove all the screws from the stern and you'll see a big hose clamp holding the seal to the intermediate drive. Mine came off with just a little stretching and I'm hoping the new one will go on with soapy water. I hope to have all the parts next week. My only question is what type of sealant to use where the seal meets the stern. I've read to not use silicone RTV, and use NO sealant under the hose clamp part."