Sam, the Dip Stick Tube is a press fit into the block. I do not believe there is a "O" Ring, there may be a sealant that is applied to seal it.
There is a special tool that drives the tube into the block.

Iam not sure how to get it out, unless you remove the lower pan and tap it out from below.

Pelican Parts.com - Dipstick Tube Driver




Sure pricy for what it is.


EDIT:

Lookie what I found from from our Dealer in Monterey, Ca.
Mercedes Benz DIPSTICK TUBE DRIVER - 111589123100





Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works