How do I clean out the vents in my RV Dometic roof ac?

sounds like it is low on freon have someone check with gage and add more if nedded.

clean drain on roof.

try replacing capacitors. or communication cable issue to that a/c

This appears to be a low charge. you should see a 15-20 degree split between the discharge venting and the return air venting.

yes it is and you will have to order party from net.

I've not run into the problem your having yet, so I will apologize up front for asking you to furnish more information. These drain cups that I assume are little round pieces attached to the base of the unit where it meets the roof, were not common on dometic, but were common on Coleman AC units. Those are the outlets for condensation to the roof anyway, are they not?
Also, as far as gasket goes, no I wouldn't recommend using 2. We were always advised by manufacturer to compress gasket to half the original thickness when installing either Dometic, or Coleman (RV Products). Coleman at one time, had tabs under gasket that when gasket was compressed, and they touched the roof surface inside, that was far enough, which was approximately half the original thickness. Believe it or not, over-tightening is more likely to cause a leak. Stick with half original thickness, or close to it.

Shut off Any AC power (hydro) to it, remove ceiling assy (inside part) and you'll see 4 bolts going up through lower assy, and into base of upper assy (roof unit) . Remove those 4 bolts and any wiring harness connected from lower to upper unit. Lift it off. If your just replacing the upper assy, leave hydro wires hooked up to lower assy , and let it hang, while you clean surface on roof for new install. Re-install 4 bolts and tighten equally until gasket is approx 1/2 thickness it was before tightening. Re-install wiring harness plug in to lower unit etc. If not replacing, but removing entire assy (upper and lower) be sure to Marette and tape hydro wires as well as any 12 volt wires, and tuck away safely. Install a vent on current opening , or whatever you choose.

You will have to go into the Roof space and see if the Distribution flex pipe is detatched from the conduit.
Regards,DT

Check run-of on roof & see if it's been reduced lately, it may just be a plugged drain at base of unit on roof.

that may be black mold..