How often should the hose that runs thru the gimbal housing that supplies water from the drive pickup to the transom assembly be replaced?

Look at it if it's hard or cracking its time. If transom has corrosion on get one of the scopes that hook up to a cell phone and with drive off shove the scope in the hose and look to see if closed up where it passes through the transom. Bravo transom corrode and squeeze the hose closed and restrict water flow

No corrosion, totally clear. I bought a new hose. The boat is a 2001, I'm assuming it has never been changed. It seems about as flexible as the new one I just bought. Fresh water only. It's a pita to change it looks like I have to pull the drive

yes the drive needs to be removed.the job is a pita.