If what you're repairing is old and likely to continue falling apart, a new one makes more sense. If it's solid and hard to match with new ones, and only has a small gouge, etc., then fix it. If the water problem is likely to recur, you need to fix that before anything, and/or lift the existing board to see what's going on underneath.

How bad is the water damage and has the source of it been fixed?

Personally I would replace the wood and make sure the damage didn't go deeper. Water doesn't just stop at one piece of wood, it keeps going and the real damage happens where it collects.

nyc_sod,
Lucy says it all.
If water is the source, repair that first.

In any event I just wanted to share with you a repair job I had at a Central Jersey Estate maybe five years ago.
They had numerous Inswing French Doors all around the ground level perimeter of the place. Most were regularly getting soaked from the mis-directed automatic lawn sprinkler system in place.The damage developed over a long period of time and went mostly un-noticed by the house staff.

What I did to repair them was scrape out all the soft and rotting wood and let it dry out a bit. Then I soaked the same area with wood hardener, as many coats as it took till it almost shined. It drys real fast.
Once the prep was done I kneeded my quick-wood epoxy and began to re-build the area removed by the scrapping. This product hardens quickly but gives you enough time to really work it into a shape and should be put on in amounts you feel you can easily work with. Its OK to layer the product - works just as well.
A few careful layers later, some sanding and the door jambs were as good as new. Primed and painted white - job done.
I mean if you have the patience, you could do it with QUICKWOOD epoxy. Otherwise, rip the whole door and jamb out and replace all the bad wood. Whats' easier?

Good Luck

All the best, The PorchGuy

Here is a link that might be useful: My Album

Sounds familiar, I've used car body filler, guess that's what bondo is. But, not for a door jamb, just of exterior trim high up where gutter back flow has damaged trim.

The only hardener I've used is one by Minwax. Is there another brand, that cost less, generally available? I get the Minwax hardener at Home Depot.

You don't need to buy the wood hardener. All it is is laquer. Buy a can of laquer spray paint--hardens the fibers right up.

When I do this, the FIRST thing I do is apply liberal amounts of clear wood preservative to kill the bacteria in the wood. Let it off-gas for a day--spray with laquer paint--bondo. If you don't kill the bacteria, the patch will fail.

I've repaired lots of rotten wood with this technique as I had lots of rental property, years ago. I never had one patch fail.

Use antifreeze mixed with both boric acid powder and borax powder (20 mule team borax) to prevent new wood rot. Recipe is about 2 parts antifreeze to 1 part boric acid and 1 part borax. Bring to boil briefly and it is ready to paint into the exposed wood. Do the cooking outside the house. Let the wood dry before painting. I'd do this whether or not you choose to take the wood putty repair route (paint the remaining wood) or replacement of wood route (paint the new wood).

Here is a link that might be useful: Antifreeze/boric mixture

"You don't need to buy the wood hardener. All it is is laquer."

No, it is acrylic resin in solvent, NOT nitrocellulose lacquer.

It penetrates much further into soft wood then lacquer does, providing a solid (and compatible) base for further repairs.

I just noticed we have this type of damage at the bottom of our front door frame as well. The way I noticed is that rain water now leaks through and into the crawl space. There is no awning and we have a storm door, so water does not hit the door itself, but it runs down and hits the frame, which over time has had rot.

I poked at it and now see that the previous home owners did a partial wood replacement, then clear silicone around the various seams. The seams have now failed in places and the water runs straight into the crawlspace.

I'm wondering if a second fix would be sufficient, or maybe just caulk/seal the seams again, or think of a more drastic solution like an awning or new door frame.

andreibd:

The rotted wood is a symptom, not a cause. You need to abate the source of water causing the rot before performing any repairs.

Thank you both. My issue is that I can't figure out the best way to abate the water problem. An awning is not really practical with the architecture. I think I need to add some pictures and see if you guys can help me with any suggestions short of an awning, or awning ideas.