If you have cast wheels, you could have leaks threw the casting. I know racers that after remounting slicks have put silicone seal on each screw divit in the tire bead, thats if they use screws in the wheel/ tire to keep the tire from spinning at low tire pressure.
Some guys have had luck by coating the inside of the tires with Dawn dish soap. I have spray pianted the inside of cast wheels to seal them.
We race with 31" or 33" tall tires, but always put the 31" tires on the car with at least 10# for towing, because our chassis support is set-up for the 31 tires, even towing 900 miles, with no problems. My tires leak some between race events, just put 10 # in the tires when towing, and at the track we always put more pressure in the tires than what we will race with, before we leave our pits to go to the staging lanes, and lower them to the pressure I want to race with as the driver is getting suited-up. When it very hot and sunny I use tire covers in the staging lanes,to help keep the pressures equal.
What kind of tire pressure loss are you having ? Because of the low pressures [ 5-7 lbs] slicks just seem to lose some pressure, it's not like you run 30-40 lbs like your street car tires, which does a better job of sealing the tires to the wheels better.
I hope this helps.
Jon
