Yes, replace the reciever dryer too. If it was me, I would only remove it,
and bake it on the barbie. This, to drive off the moisture that is inside
the dissicant bag,inside the reciver/dryer. Then, when no one is looking, I
would replace it(not!,well maybe).

I understand that the ideal new oil content for a 134a system is: 80
percent new compatable oil.You can never get all the old oil out.

Also, the molecule size of a 134a molecule, compared to a R-12 molicule is
like a golf ball , to a basketball. The golf ball being 134a. This is why a
barrier hose is needed. However, an old hose that had r-12 in it, is spared
from  this exodist.  The old mineral oil that has seeped into the rubber
acts as a barrier.

 PLEASE BUY DIESEL PARTS !