Are these things breathers? The back one on my 97 XP has oil coming out. The red cap is gone too, but the oil issue was there before the red cap disappeared. The red cap disappeared today, I found a couple small pieces of melted plastic.
They are rave valve caps, if they are melted you have damaged rave valves, bases or o-rings, at any rate you need to tear the whole rave valve system down and get to the root of the problem