I cannot relate with you on deep mud riding we dont do it...But If the box is sealed properly no mud or water can get in under normal operation , just the dusty air from where the actual box breathes inbetween the seats in the secondary box..(Gen 3)The problem we had with greasing the lip is it attracts dirt..We do not mud ride so the only time we open up the air box is for a good bath. Just as with a Motocross bike ,in extreamly dutsy to powdery conditions I may change the filter during the day. Rare with the RZR...The Uni filters work, its only enemy is water and neglect..I am sure ,as you know the stock paper unit is junk it cannot handle dust ,dirt, or water..Silicone for us..
My 2 cents