The dipstick tube bolts to the back of the right cylinder head and bolts to the side of the transmission. Remove those two bolts and pull the dipstick tube up and out of the car. At most you'll need a new o-ring between the tube and the transmission.

I don't think something 6" long will slip into the transmission. If it's a single 6" piece it should be okay to leave it in the pan if it does slip in. My concern would be that there are smaller pieces and perhaps something that can jam moving parts.

Maybe you can lift the tube off the transmission slowly and grab the tip as soon as there's enough of a gap.

Is the dipstick magnetic? Can you run a flexible magnetic retriever down the dipstick tube?

Sixto
87 300SDL