Dead A/c

I don't know a lot about A/C systems, but while trying to trouble shoot mine, i found that the low pressure side "filling" valve had a leak.
I found the A/C didn't work this spring and that the pressure was low. I put a can of refrigerant in, and it worked for about 3 days, then it was low again and not working. While looking at the system for oil spots, (leaks), I heard a slight hiss from the valve. I tapped the valve pin to reseat it, but it still hissed. I put an O-ring on the stud of the cap, added some more refrigerant, and it's still working after 2 weeks.
Is this a good fix, or what would be recommended? Is this common?
Thanks

If it works then its good. A/C systems are expensive to get fixed, so anything you can do to get it to work is the best haha