I was going to change the impeller as its old but this one doesn't have the window on the exhuast housing to disconnect the shift rod. Its underneath the powerhead and apparently ya have to pull the powerhead off to disconnect the shift rod to drop the lower unit. Anyone ever do one? How hard is it? Any pointers or words of wisdom? Do I need anything other than the impeller, a new gromet for the pick-pu tube and an o-ring for the top of the shaft?