Guess that depends on where and what size your motor is so far as preference to ss or alum. and what kind of waters your in? Mine stay dinged up, however I have been lucky and beat my stainless back into shape. Mines an outboard and can definatley feel once I "whacked" mine good. I run a lot of low rocky rivers. I do carry a spare. Main thing to look at is make sure its not leakng oil. As I banged mine really good one time and continued to run. I could really feel the out of balance and it wore a seal out in my lower unit$$