I've had the same situation, new tires on old rims. I clean the surface perfect and the beyatch still leaks after a week sitting. Slime has fixed that 75% of the time. The times it didn't, the rim was bent bad or the bead very chewed up from dismounting. I do run slime in the majority of my tires.
Honestly, I usually buy the whole package of good tires on thick rims and have far fewer problems. Guys just tear up the bead removing it....
And, I've never had a tube last more than a few months because the valve stem rips off even at 8psi. It must just be my aggressive riding but tubes do not work for me.
All our government does is distract us while they steal from us, misspend our tax $ and ruin our country