A few years ago I had a 9.9 Merc, and had to switch the impeller. Now I have a 25, and it's due for a new one. Could it be much different? My 9.9 was an early 80's model, and my 25 is a '01. Didn't know if much has changed in years, or Horse Power. It's something a do it selfer can handle I believe. Or do you guys reconmend taking it in somewhere?