C160 Hydro dipstick being stubborn!

[Gary S Minnesota 61]

Hi All,

This evening I pulled the hydro dipstick in order to check the transmission fluid level on my 1975 C-160.  (the decal says to fill with 10-30 0il to full mark).

Now I can’t for the life of me get the rubber grommet/gasket to slip down into the fill tube.  The tube on this unit appears to be plastic or nylon so I’m afraid to get too rough with it.  I did apply a light coat of oil to the rubber surface that slides down into the tube but that didn’t help.  I’m thinking that the rubber has probably gotten hard with age. Are there replacements available?  Or any suggestions?

Thanks!y