Hello Joe,
The seal directly behind the impeller may not be the source ofthe leak. I am rebuilding an engine from a 2000 SRX and found the water pump impeller shaft on my engine to be corroded also. Members of this site have told me that the source of the leak could be the seal waher under the impeller bolt, these seal washers are a rubber coated metal washer that are prone to failure, especially if the impeller is not a snug fit to the shaft. I believe these seal washers need to be replaced everytime you remove the impeller bolt. I was also advised to apply green loctite to the impaller shaft before installing the impeller to prevent the impeller from wobbling on the shaft and wearing the seal washer. You may want to try replacing the seal washer first before changing the impeeler shaft seal. If you do need to replace the impeller shaft seal, the trickiest part is the removal of the old seal from the lower crankcase half. I removed this seal by carefully using a scrwedriver to push the edges ofthe metal seal away from the case towards the impeller seal. I worked my way around the seal until it was loose and removed it with a needle nose pliers. I would then clean up the rust and corrosion from the shaft and reassemble. You will need to use a a deep socket, perhaps for a 1" bolt to push the new metal seal in place.
