Those Dorman boots are plenty tough. The first one went fairly well, but the second got hung up with the small end stretched on the funnel only about two inches from the bottom. Had help from my wife, but we couldn't get it to slide. It stayed stretched like that for about an hour until I took a flexible putty knife and sort of bent it so it contacted the top of the boot the width of the putty knife and pushed the boot around and down until it finally popped off. Lubrication seems to be the big issue- got to get it to slide- fast.
What's the best stuff to use- how about ky jelly or astroglide?
Actually..I have some Ruuglide (tire changing lubricant) but didn't even think of that. I wonder if that would work? Might work on the boot but melt the funnel. If I could get a metal funnel.....
Rick