I know many say, "don't" but it has obviously worked all this time for you so why not? I had a gooseneck on my 5th wheel for 14 years without any problems. I bought a new 5th wheel and truck and wasn't sure if it would clear the cab and at the same time I found a PullRite auto slide for $500. so I went that route. Do I need it? I don't know but I don"t worry about my cab although I admit I've been considering switching back to goose neck because the hitch is so heavy and old age has caught up with me.
The Reese gooseneck and using another extender put the ball at the same angle and distance so I would not be afraid of using your old extender. Reese is owned by Lippert so they say their's is the only one they will warrant. your warranty is already expired so there is no difference there either. My warranty too has expired so another reason for me to switch now.