"Have you looked at the sub floor, joists & band board / rim joist
yes, I've removed the threshold & the sill. The rim joist below is ok
as are the redwood sill supports that I installed in 1980.
"If the visible material is as far gone as you describe, water has been
infiltrating for a while."
The fornt door area is unprotected and the rain that hits the front
step (brick landing about 3' x 4') splashes onto the sill & the door.
I should have said that the sill material is deteriorated on the top &
front surfaces only the decay does not go through the sill. On the
bottom side of the sill the wood is still sould
"Consider a way of protecting the new sill."
We've considered an awning but my wife is not sure it she would like
"Is there splash back fromthe surface outside, or is it unsheltered
from the rain?"
yes & yes, but in SoCal we really (usually) don't get that much rain.
What wood species do you recommend? Oak, teak, mahogony (sp?)
I don't think you can just go to HD or Lowes and pick up a new door
frame. You need to make one youreslf. The approached used in my
neighborhood is to replace any bad pieces of wood individually. If you
don't have an awning over this entrance, then getting one should help
prevent wood rot in the future. Storm door also helps. I have both on
all my exterior doors and the vintage 1950 wood is actually in pretty
good shape in most places.