perhaps the best thing you could do is run down
to your nearest VW dealership and get some "originals".  I think it was
$160/pair at our local dealer.

Hello,
I bought 4 years ago 2 brand  new mirror from Vw dealer (Expensive)
have the same swivel problem

moving all time on highway or when you closed the the door

its easy to fix
take apart the mirror
remove the black paint of the round part of the mirror (base)
make the surface more rough  ,
make some nick or scratch to get more friction between the two parts
and and few washers between
the bolt and the spring  and tight , but not to much

 no more problem
 cheap fix for expensive mirror.

Denis Belisle
Saint Basile le Grand  Quebec ,Canada
fresh paint  westie 85