im no expert on vehicle AC, But google a d youtube AC Schrader valves.
Apparently its common for them to leak, and you can buy new schrader valves for cheap. Need a schrader valve tool to remove them, that too is cheap to buy.
So before you go spend a lot of money on AC repairs, google/youtube schrader valves.
I too have an ac leak and i suspect it might be both the high and low schrader valves.
i need to buy the valves and tools, and if it works, i can try an AC recharge kit next month on my 20 year old suv Nissan 2.5L.
Apparently, mechanics often realize the valves leak, but can be sneaky, charge you for hours of labor , pad the bill, and replace just the schrader valves, with the customer unsuspecting.
just saying.
I do not think they will be able to change the Schrader valves without loosing the charge, and then having to recharge the system.
Some inner tubes have a cap that doubles as a Schrader valve tool. I have one on each of my bikes so I do not have to carry the tool with me.
You can change out the Schrader valves without losing the refrigerant charge or evacuating the system with a special tool like this Lichamp Valve Core Replacement Tool.
If you can't change out the valve core (or the valve core threaded interface is damaged), replacing the plastic dust cap with these Dorman 902-025 brass plugs and Teflon tape will prevent the refrigerant from escaping.