My 8 yr old tag Heuer watch stopped keeping accurate time and is gaining 5 minutes/day. Where do I send it for repair and at what cost?

You can fill out a repair form on their website or call the toll free number (also on their website) and arrange to have it shipped in for a service/rebuild. I had 3 Tag watches serviced by them in 2019, and every one came back on like new condition!! 👍

Repair can range from 100 to 300 it probably needs a service you can find this information on their website Tagheuer.com