Dont know the 411, I have a 2001 bene 473, at a wild guess the stanchions cannot be too different.
The stanchjion base has a threaded stud passing through the deck
with a large washer and nut on the underside, sorry, cannot remember the size, think the nut was 19mm, not 100% sure on that one.
The stanchion itself is just held in the base with an allen headed set screw.
Your biggest issure will be access to the nuts, I was lucky, they were all pretty well accessable, you will probably have to pull some headlining away and be prepared to stick it back on again.
I used the sikalflex sealent under the stanchion base and a bead around the hole for the stud. Dont put sealant
on the stud or backing washer, if the topside losses it water
tightness you'll ant to know about it. If you seal the inside, and the top side leaks
, the water
can work its way into the deck core
You'll notice a plastic/nylon insert set into the deck which the stud passes through, make sure that is in good condition