Dipstick won't go back in

pull the dipsticks out of your daily driver, your buddies car...whatever you have access to. see if any of them go all the way in.
you're clearly hitting a shelf on the block, or the tube isn't seated all the way. something. if one of the other sticks go in...make yours look like that. (angle, edge sharpness or roundness) etc.

hard to believe a stock 40 year old dipstick, in a stock 40 year old pan, in a stock tube...is "all of a sudden" not going back in. your previous owner either knew something was up...or...after dealing with this himself for so many years, figured out the correct amount of "holy hell" to give that thing to ram it home.