Repairing post sunk in wall

[cuboid]

This post sunk in wall has come loose. Was told as post has rotted probably its best to put a repair post in by digging out part of wall. Don't want to damage wall though

 

[ptarmigan]

Is it a 4 inch post,all i did with a rotten one was to remove fence panels either side where attached to rotten post and drill out the rotten stuff with an auger or wood twist drill and whack the new post in after soaking in old engine oil for a couple of days,having taken a second look at the pic what is the piece of wood behind the post that the gravel boards are attached to,perhaps a picture from the side showing that part.

 

[lonner]

as above or use a post plate and screw to wall,after cutting off old post,
then fit post .

the above option is going to be relatively easy tho.

 

[cuboid]

Is it a 4 inch post,all i did with a rotten one was to remove fence panels either side where attached to rotten post and drill out the rotten stuff with an auger or wood twist drill and whack the new post in after soaking in old engine oil for a couple of days,having taken a second look at the pic what is the piece of wood behind the post that the gravel boards are attached to,perhaps a picture from the side showing that part.

They're not panels. It's featheredge or whatever they're called attached to rails. The bit of wood I guess bridges gap between post and gravel board I think. So you don't think drilling out more space ad inserting one of those concrete support post things