I have a coast valve, I took it out and adjusted the thing so it did not send me into the roll cage... There is an adjustment on the valve where the coast valve goes, unscrew it a few turns and problem solved.
Adjusting the servo has nothing to do with the hold back.
Regarding the snorkel, the air filter does not get that dirty.... I'm not sure I could justify the cost of the snorkel just to increase the time to change the air filter....
Changing hydro fluid in my opinion made no difference.
Wayne