My slow leaking tire is bothering me

Hi,

Here is my problem, each time I get my tires changed then I will have slow leaking problem on one of my tire. It is always so called dirty wheel causing the problem and once it is cleaned then the slow leaking is gone. The slow leaking is something like loosing 1 psi every one or two weeks or so. I am thinking instead of going back to the dealer every time and spend 50 bucks to clean the wheel (rim), how about I get a small or portable machine so i can add air by myself?

P.S. I live in Quebec Canada, so by law I have to change tire twice a year.

Thanks for any input!