Older motors will see significant crankcase pressure due to normal blow-by. The high pressure in the cylinders seeps past the rings into the oil galleys, and pressurizes them. On some older cars, the oil dipstick blows out of the dipstick holder from the pressure. The fountain of oil that follows does not help the engine bay stay clean.
Solution 1: Buy a new dipstick from the dealer. The rubber on the old dipstick can't hold the dipstick into the tube. The new one will have a softer, tighter seal.
Solution 2: If that doesn't do the trick, use a nylon "zip" tie to hold the dipstick in. Note that if you have this much blow-by, your motor is probably about due for a rebuild.
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