Be careful with fix it in a can .It can really mess up wheel Balance with gel, liquid rolling around. We sell quit a few tires a year and see this issue often. Ussually it is corrosion at the bead or around the valve stem seal - Where it seals in the rim.
Locate the leak yourself with a spray bottle and diluted dish soap (2 or 3 capfull in a quart) . Fill fhe tire properly and spray down the whole tire and rim- leave it sit for a few minutes. ( Not long enough to dry out keep it wet). If it is a porus rim or bead leak/valve stem seal you will see a fist full of bubbles. Now you will know what to address.
We use a special low speed die grinder with a wire wheel encased in plastic (so the wires don't fling out) and buff the corrosion off. After you buff the rim you must seal it up , we use a rubber type cement and paint the bead and valve stem area where it contacts the rim. (Mag rims may need to be sealed with clear before rubber sealer and skip the rim buffing if there is no corrosion) Make sure you clean the tire bead with a wire brush and solvent . All of this can take a bit if time. Many tire guys don't have or take the time to locate detail clean and prep a rim. This could take quite a bit of time. A entry level tire buster can't spend that much time on a leak. We deal with corrodeing aluminum rims and flaking chrome quite a bit. Magnesium rims are a rarity now a days but done properly I cant see how it could hurt to save a rim for street use. Opinions may vary.
JerrySr
#2636