When I have my in-warranty routine services done by an independent I always specify it has to be a log book service. My independent provides an invoice that line items every manufacturer recommended/required service for the interval. One year the requirement included replacing perfectly good expensive platinum spark plugs, but replacing them was required to avoid potential issues with the manufacturer should I have subsequently needed to claim.
Ultratune should be asked to provide their own ‘guarantee’ their work would be acceptable to VW as regards the VW warranty. Words are cheap, repairing an engine when the unexpected happens and the warranty is considered voided, not so much.
As has been expressed, service intervals are kilometres OR time whichever comes first, and some items degrade over time regardless of use or lack thereof. Some items are not as germane such as a pollen filter; my dealer once declined to change it per schedule since it was a $65 item they documented looked like a new pristine part, but that was the dealer not a third party.
FWIW there is a report on the Community about a dealer using unapproved transmission oil that resulted in poor shifting and neither the manufacturer nor dealer took responsibility.
Considering the cost of repairs if ever required, follow the log book and whether maintained by the dealer or an independent, be sure your invoices show full logbook services. All reputable mechanics subscribe to services where they have full details of service requirements.
