I'll be replacing my old sliding patio door soon. It is a standard sized
patio door and I'm getting the door from an Andersen retailer. My friend
and I will remove the old door and replace it with the new door.
The new door's RO is approximately 3/4" shorter width-wise than the door
there now.
I'll need to fit it correctly between the studs with shims, etc.
I'd like to purchase all my finishing wood before I start the job but I have
this feeling that in order to see what is really behind the edges of the old
door's track (i.e. wood condition and size/thickness) I'll need to wait
until I pull the old door out.

I am particularly worried about the sill. Are sill widths pretty much the
same or again I should wait until I pull out the door track and see exactly
the width? I need to replace the sill as it is beginning to rot on the
outside edges. The thickness is 1 1/8".

Thanks,
Walter