Question on service

Just purchased a 3706 Spitfire black dial , a pristine late 2006 model that althought keeping time to the tune of 3 seconds/day, has never been service...
Time keeping is so good that I'm hesitating to send it in for a rehaul, thoughts from those that may have serviced their IWC's? what is tipically a rehaul cost and what is included?

If it's not broken, you don't have to fix it. That is how I'm handling this.
Replace the rubber sealings and have the waterproofness checked. A few drops of oil and a small review by an experienced watchmaker who is available at serious watch stores. That's all I would do if it's running properly.