On my previous camper, we had all 3 crank-open roof vents and the skylight over the bathtub get beat-out by hail. I didn't catch it for a couple days, so things got pretty wet inside. Mine were not just cracked, they were broken clean out, with chunks missing from the plastic.
I used massive amounts of duct tape to seal the gaping holes and keep the rest of the plastic from falling out. It held up pretty good. I avoided more leaking.
The upper bunk was soaked, the kitchen area floor had a puddle in it, water standing in the bath tub, and the master bed was soaked. But!!! everything dried out. No damage to anything in the walls or anything else. The vent frames themselves are sealed to the roof so no water intrusion occurred in the roof or the walls. It just puddled and made stuff wet directly under the vents.
Fast forward a few more hours and I called my local dealer and told them what happened. They gave me an estimate (over the phone) what it would cost to replace every roof vent and the skylight. Because I duck taped everything so well, I didn't need to be in a real rush for an immediate repair (which was good as we had more rain) later. I set up an appointment.
I also had them to price me a knock-off Max Air vent cover for each vent and also replaced the fan in the vent in the bathroom as all the blades were so brittle, they broke off.
At the scheduled time, I took the camper in. 24 hours later it was ready for pick-up and was less than $250 for everything! I considered putting a claim on my insurance, but I have a $500 deductible, so that just didn't make any sense.
My suggestion, tape up the crack and fix up anywhere it's leaking. Let the camper dry out, and then simply replace the vent. It's a job that not so impossible the average Joe-Smuck can't do it, if you've got the time, effort, and energy, and not afraid to get on the roof.
You always have the option to take it to a repair shop and have them fix it. Unless you've had previous water intrusion on your camper, a one-time leak thorugh the roof vent isn't going to seep into anything except what is directly under it. Now, if you've had problems with water intrusion in the past, then you may have a problem now. But getting wet once, drying out, and moving on won't mess anything up.
If you put an insurance claim on it, you'll need to take it to a repair shop anyway. So why not have them check for water intrusion when you get the vent fixed. That's what I'd probably do.
