It may be worth filling the system with dye-containing refrigerant to verify it's leaking at the receiver/dryer (sometimes called accumulator) and not elsewhere. If there is a real leak the bright dye will disclose it. The dye doesn't always work well if the leak is very small.

The job is not hard, except that the fittings may be seized or rusted. I presoaked em in solvent for a day or so.

Also you need to account for the PAG oil which is or was inside the accumulator so that when you put it all together you have about the right amount to keep the compressor lubricated.

The other issue is that once you open up the system you need to evacuate it very thoroughly before filling it. Any air or moisture left in will lead to things deteriorating quickly. It may be hard to find a strong vacuum pump that is designed for this. You could replace the accumulator then have a pro evacuate and fill.