I took a good look at mine. The raised collar is there only as a short remnant, appears the tube riding close to an after market header ran it hot enough to shrink it, and likely harden the rubber causing it to shrink and fail.
The metal "cap" of the dip stick is loose enough to slide up and around the handle (round finger hole) of the stick allowing the plug to be slid onto the stick above the washer and the cap returned, and the shape of the handle restored.
This can be accomplished IF a new rubber plug is flexible enough to slide around the handle and over the swedge that retains the cap in place without damage.