starter solenoid sticking

When I crank the starter it doesn't disengage every time. But if you crank it and tap the solenoid it will disengage. My question is not if this is bad or not but rather can I use any solenoid or do I have to use the direct replacement. I would rather use the one I have laying in the basement. Thanks oh yeah I think the motor is from the 80's 50horse.