i dont know where you get the idea seals are going to dry up,my truck runs great on propane,never leaks,has tons of power.its all in the way the conversion is done.just like any motor modifications,you get people that know what they are doing ,and idiots that should never open the hood on anything. i run a 428 SCJ on propane in my 74 4x4 dually,i pull a 38 foot tri-axle enclosed racecar trailer that is over 11000 pounds.i dont get much passing me on any hills through the rockies.my engine was 425 horspower new in the crate,it is now more,but ive done more work to it.the truck was chassis dynoed at 428 horsepower (to the ground).i would never go back to gas again.i may go to a deisel engine one day,but im happy with the propane.