I think it really depends on your dealer & how hard they will push MGNA. My dealer ( MPH ) replaced my front rotors & driveshaft under warranty. The front rotors took awhile ( 2wks ) I wouldn't think you would have any problems , regardless of the dealer. The rear seal failing that soon is obviously a factory phuck up, and I can't see how any of your mods would have an affect on the rear seal.
P.S. MPH also replaced my tach too. A lot of the same stuff has been replaced by many here & not always with the help of a dealer. I know for some the bottom line is the price of the bike, but for me having a top notch dealer has made owning a Guzzi a pleasure