What brand of synthetic oil are you using? (IE: Amsoil says you can use their 5W 30 for a year or 25,000 miles, just change the oil filter after 6 months & top up). Synthetic oil last much longer than conventional oil for sure, but it won't last forever & the oil filter will need to be changed in that time as well.....I would at least do that.....but if you do, why not just change the oil while your at it. B)