When you have an annoying leak like this, you really need to submerge the tire and wheel to check for both leaks in the tire and for a crack in the rim. Go to Walmart and buy one of the cheap plastic sandbox/pools. Fill your water tank and then take it back to the store that last checked your tire. Explain that you are still having the issue. Tell them you brought your own pool to check for a leak and that you'll fill it with your own water.
Fill the pool in an out of the way place and then pull your coach up to a bay and have them remove the tire/rim. Now try looking for leaks with it in the pool. Make sure you check the rim for air bubbles (cracks).
On a side note...when someone does a service like they did earlier for you, I always make sure I tip the employee, at least $5.00, if they don't charge me. It makes for a good relationship later on.
If you don't want to do that, go to Harbor Freight and buy a cheap 5 ton jack and the same pool and check the tire at your house, and at your leisure.
