Scirocco Central

How important is to do that when changing the plugs or coils?

Shit I forgot to that the last time I was changing the plugs and coils..

Do I need to lube just the black rubber on coil?

Never bothered. Never had an issue.

It's not really necessary with these type of pencil coils as the rubber boot is effective enough in keeping the moisture out.

However it really does help in stopping the boot welding itself on to the spark plug stem, just smear some over the white porcelain part of the spark plug, for easy removal next time.