I picked up a new engine oil dipstick from the dealer. Here is a comparison (top to bottom) of the original 1991 G4CS Sonata dipstick, new G4CS dipstick, and a 1995 4G63 turbo Eclipse dipstick.
The seals get really hard after 5+ years. The heat really dries them out. I picked up a couple replacement seals for a couple bucks each.
This is a picture of the new Hyundai seal and a turbo Eclipse oil cap with a VERY dry seal. It snaped in half immediatedly when trying to remove it.
As you can see, the Mitsubishi and Hyundai caps use the same seals. The new seal slips right on.