what they are saying is to tape up that section of the coil packs that have the mark.
do a couple of layers.
this will "temporarily" stop them from arcing if that is in fact what is happening.
If it fixes your issue, buy new coil packs.
if it doesn't, then you didn't waste $500
the silicon option is better than electrical tape but it involves going and buying shit from bunnings where as most people have elecrical tape around.
also, while you have the coil cover off, put all the coil packs back in and at night once up to operating temps and you feel a miss etc, in the dark, pop the bonnet and see if you can see it actually arc in the valley where the coils are.
You can see it in the dark if it is actually arcing.