I just did the same to my 120 last year. Raw water pump was starting to drip and was the old style. Cost a few bucks but I got a complete new unit including gear, upgraded it to a new style which is more robust and easier to service. I actually got mine from Fredwarner1.net for about $550, complete unit. I've bought oil coolers, heat exchangers, and starters from him as well. Online ordering is easier and faster then American Diesel.
Ford Lehman 120 & 80 Raw Water Pump 2C45 D-365 Marine Diesel Engine 2715E 2712E