I beg to differ. I have just rebuilt my M96,21 and each spark plug recess has a tube and two seals.
Pelican Technical Article: Replacing Boxster Spark Plugs and Coils - 986 / 987
see fig 3.
Part # is : 996-105-325-52
Pelican list them for the '03 & '04 Boxster
'05 Boxster ,different story