New member here, must say this is a great site. I have been lurking four about a month and now I need some advice. I tried a search but had little luck.

I have a '98 454 MPI and noticed the circulating water pump is leaking. I am assuming this water pump is similar to a regular car pump when water starts leaking from the weep hole the pump is bad (fairly new to marine motors). If I need to replace it where should I go. I know the part number from Mercury Parts Express and found a OEM pump for around $160 on the web but wondering if I could get the same part from NAPA. This was a salt water boat but now it will only be used in freshwater.

JBH

Try www.basicpower.com They have a brand new pump for 109.00. I bought one for my 350 for 85.00.
They have the best price I could find.

Napa has automotive AND marine water pumps. I have two on mine and they are cheaper Merc pumps. Just be sure to specify marine.

Isn't the only difference between Marine and Auto the stainless back plate?

No, the ones I seen also have a cast iron impeller not stamped steel and also brass plugs for heater hose connection.
The stamped steel impellers will rust out rather quickly when not protected by antifreeze. If you have a close system you can get away with it for a while.

I was told the marine pumps have a bronze impellor, stainless input shaft and back cover as well as ceramic seals.