hi
i have seen the damage these can do and its not nice.
the last one i did was a 320 compact with 80k on it. swirl flap from number 4 cylinder had fallen off and embedded its self into the piston crown and then continued to smash into the valves and head. after a lot of time cleaning and machining she ran again but cost in excess of £800 and i am told it was very cheap.
my own x5 is a december 05 and does not have swirl flaps. i first checked on real oem and confirmed by looking on the manifold.
they can be seen quite clearly if they are there but is obviously harder when they are not there as you cant see them so dont know where to look. 22mm is the common size on most i have done. i did remove a set last week from another compact and it was just in time as 3 were loose and about to fall off.
hope this helps
dave