stuck dipstick!

i have a puzzling problem. i want to change the o-ring on the dipstick tube of my 727, but iv'e undone the bolt into the 383 block that hold the dipstick retaining bracket, and the dipstick wobbles around, but no amount of pulling will remove it. there are no other bolts holding it, it must be the existing o-ring in a groove that's stubborn, any ideas? thanks Gerry