I know there are other posts on here regarding removing a dipstick tube whether broken or not. Just wanted to share how I removed mine yesterday. I wasn't sure if mine was broken or not so I wanted to remove it to make sure the flange was on the tube and it didn't get pushed all the way in once I installed the Lokar tube and stick I got for it.
I recently went out and scared a bunch of dove with my shotgun and was about to clean it when I thought the cleaning rods look just about the right diameter and length to get all the way through the tube. Sure enough it was a perfect fit. I then found a small bold with the head diameter being just small enough to fit through the tube then put pressure to the side and pulled the tube right out.
I can't tell you want size the flat head bolt is, I was lucky enough to have one lying around, .303 was the size of the head. Just a another option for those out there dealing with removing their dipstick tube.