Replacing Turbine Vent

Ok, I know how to do it generally, and it isn't really very complicated. But, Does any body have any tips on getting the new one down over the fluted end on the roof jack? That is the place where I always have trouble. It is almost like trying to get a 12 inch vent down onto a 12 1/4 inch jack. I know it is just supposed to slip down onto it, but I always have trouble with that kind of slip joint.
Thanks, Bill Gill
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