Like Craig said, use some Simply Green or mild soapy water and without spritzing too much, soak the bead and tire tread areas while slowly rotating the tire. You may need to pump the tire up some towards the max PSI or a bit more. If your spray bottle does a fine spray it may cause air bubbles on its own, need more of a slow stream of soapy water. Do not use any harsh soaps like Castrol Super Clean as it does not like aluminum if left on long.Find an old spray bottle and fill it with a soapy water solution. Air up the tire and spray the water on it to find the location of the leak. You should see bubbles. Be sure to spray some of the water in the stem to see if the core is leaking. And spray it around where the stem goes through the wheel. If you want to take the wheel off the bike then put it in a tub of water and look for bubbles. Just don't get water in the bearings.
Unless you or your dealer has located the source of the leak then it is not for sure that you need a new tire. You might just need to tighten up or replace the valve core. Or you might need to replace the valve stem.
How much is a plug likely to cost?I would have a hard time trusting a dealer that is selling you a tire and he doesn't even know why it is leaking. As has been said, it could be a valve stem, valve core or even a leak around the rim. Also, I have plugged tires on cars, motorcycles, scooters and lawn mowers for years and have not had problems. You can plug them if the leak on in the tread area but not on the side or sidewall.
ps. I worked insurance claims for 31 years and never saw a tire plug exclusion in any policy I have ever read.
My Burgman 650 rear tire had a slow leak (around half a pound per day) for years. Changed tires at 10,000 and 22,000 miles, replaced cracked valve stem once. Nothing fixed the slow leak.My rear tire has picked up a slow leak. My dealer says that his insurance won't let him plug it. He's ordered a tire for me, but it won't come in until next week.
That Fix-a-Flat stuff, does it work for motorbike tires? At least to tide me over?