Our previous Catalina was hit by a power boat and two stanchions were bent as the bow road over the gunwale.  Catalina Direct had the exact replacements. You've indicated no visible deck damage which is a good thing. The decks are pretty thick and tough. Check the inside cabin area around the stanchion nuts for stress too.
The stanchion replacement is fairly straight foward. It will go better with one person on the outside and one on the inside to stop the bolts from rotating while the other applies torque to remove or replace. I prefer polysulfide boat caulk to re-bed the bolts. Some like butyl tape. However, caulk will seal the deck surounding the bolt as well as exterior and interior faces. Clean the bolt holes of any previous caulking. Be sure use a drop cloth inside the boat to catch any debris or dripping caulk that oozes from the bolt holes. Polysulfide is messy- you will need plenty of paper towels. Wipe excess caulk  away after torqing the new stanchion bolts . I think acetone might help clean up excess caulk, but use sparingly. What is the appropriate torque for the bolts? It is probably in some spec somewhere. You need enough to be "snug" but not so much that you are crushing the deck laminate. 

Its not a bad idea to look at the deck core after you've removed the bolts- check for voids or wood softeness from water intrusion. If any is evident, let the wood dry out, remove any deteriorated rot and and rebuild with epoxy. (you may have to re-drill the the hole). Our Catalina 30 had plenty of voids- especially around the cut outs involving hatches and windows. I always used a hatch removal as an opportunity to fill the voids with epoxy and seal the edges of the wood to minimize water intrusion.

+1 to Paul's comments above.

I've not replaced damage, but have re-bedded the vent stanchion on the port side when a survey found the deck had moisture last fall.  I removed the stanchion, used a Dremel to route out the core, and rebedded with butyl tape following Mainesail's excellent, illustrated guide: http://www.pbase.com/mainecruising/boat_projects.  While at the project, I used the opportunity to re-route the holding tank vent from the stanchion to a normal mushroom through-hull vent just under the rub rail.  I filled the large hole with epoxy and glass cloth, and cut off the stanchion base tube rather than buying a new plain stanchion.  The project went very well, and the most time-consuming part was the epoxy work.   I like the butyl tape rather than one-part caulk as it forms a good seal and is easy to work with, but to each his own.

Physically removing and replacing the stanchion was extremely easy - four bolts and some fender washers.  Having a helper on deck or under is crucial as everything is through-bolted (I think).  There were some stanchions farther back that are screwed to the embedded aluminum plate (figure available in the owners manual for location).

I like butyl over poly. If you want a life long repair drill the top holes to 1/2 ". Then using a small router bit route the core by 1/4". Tape bottom holes and fill with epoxy.  Then redrill holes and put a good countersink on the top hole    MaineSail has good description on marinehowto.com

Les