Looks like it doesn't appear using the camera view button but when you put it in reverse it should be there. I just checked mine and it's shows up when in reverse. It works great too.
I tried to figure it out when I first got it and then forgot about it. After driving some gravel roads I noticed when I was backing up that there was a different icon on the screen in reverse. I pressed it and it washes the camera. I'm not sure if it only comes up when the camera is dirty...
I used it this afternoon with my utility trailer (4pin) and it worked fine. I'm almost positive I used it in the past towing my camping trailer (7pin).
I'll have to test it out next time I take it out.
I would just change it. I'm already under the truck and it cost around $5. That's a gallon of gas around here. It's worth it to me to know it's as clean as possible.
I've used it quite a few times and have had a great experience with it. I thought I never would use it but it's one of my favorite things on the highway.
I drove 21 miles from Paradise WA to Ashford WA and got 76.6 MPG with this one weird trick. Gravity. Seriously though it was pretty amazing watching the numbers keep going up.
Paradise is over 6K feet up Mt Rainier.