How can I tell on my Revo Rocket which Gen model I have? I bought it a number of years ago. I’d like to know for maintenance and repair purposes. 
 

If you have a switch under the side plate that allows you to take off the side plate it's probably the Revo 4 based rocket.  If you have a long screw that goes from the handle side to the palm side to hold the palm side plate in place it's the older rocket. I know you said you bought it a few years ago so it wouldn't be the gen 5 rocket, but that one has a straight handle instead of a swept in handle.