I can only respond to the use of paper gaskets in the sink drains...
the gasket may have been mis-used, which I have no answer for....
but there IS a paper gasket/washer supplied with the rubber seal, to be used with the drain basket assembly in the sink, but its supposed to fit between the nut and the rubber gasket....
after the drain basket is inserted, install the rubber gasket, then the paper washer, then the nut....
the paper is used as a friction washer ("anti"-friction washer), and is usually necessary to keep the rubber gasket in perfect alignment when installing it... otherwise it would be pulled/squeezed/forced outward as the friction of the nut pulls on it when rotating the nut to tighten the assembly in the sink basin....
as for the other problems you are having, NEW RV units are the worst for having issues like you are experiencing.... the work force in the factories are not much better than any of the young aimless adults in your surrounding neighborhood.... and for this type of employee, there needs to be about one supervisor for every 3 workers, but they dont, and will never employ that many supervisors.... so we get what we get, and unless you are willing to spend closer to a half mil for an rv that during the start of the manufacturing process, they designate specific individual inspectors for every individual system in the unit, which then has to be signed off on after TESTING and completed to satisfaction, it isnt going to get any better for us who buy these units.....
EVERYONE i have ever known that purchased a new unit so that they wouldnt have to put up with a previous owners issues, repairs and problems, has ended up with more issues that I ever have, and I have always purchasing USED....
its my opinion that a good clean, well maintained, used RV is always a better deal than a new one, in every respect, because it has had the bugs worked out of it, whereas the new units ALWAYS has a problem(s) somewhere.... and you, as the purchaser has to deal with the issues because you are the first one to ever use all the systems were not "used" previous to you buying them.... they may have had a quick test, but they have not been used like the buyer will use them.... so until the unit is purchased and used, no one really knows if there are any problems or not.....