Re: 1976 115hp 1150 Mercury Thunderbolt
Aaron, this site does sell parts.
The one I use regularly is
www.boatfix.com
Good prices and they ship promptly. They also have a cross-reference from OEM part numbers to Sierra aftermarket parts.
This site is pretty handy for looking up OEM parts:
http://www.dougrussell.com/partscatalog/collections/index.cfm?fuseaction=collectdetails&colid=01
On the lower unit oil, it could indicate water intrusion. Most likely places on these are the driveshaft oil seals in the water pump base, and the shift shaft bushing assy oil seals.
Change the oil and then check it periodically for further contamination, if so something's leaking.
If you want to do some preventive maint while you are replacing the impeller, you could pull the water pump base and replace the 2 driveshaft seals. In addition to the seals you'll need the pump base O-ring and gasket.
If you have a source of low pressure air you can pressurize the lower unit (12 psi max) thru either the oil vent or drain hole, after draining the oil, to check for leaks. Prepare a soap solution and spray or brush on the (3) shafts' seal areas and any leaks will bubble right up. Sometimes if you turn the shaft a bit or wiggle it to and fro you'll catch a pesky leak that otherwise wouldn't show up.
HTH..........ed
