I've never seen those service agreement situations ever really work out for the owner. Seems to always be language that would deny any real repairs. You have a leak. That is likely documented. These systems should not leak. It should have been addressed 6y ago, somehow. IDK how many lbs they are adding, but you're probably like others where you don't call until it finally won't do much, so that would lead me to think several lbs of gas.
What I might recommend is uploading a private vid on youtube and dropping a link here so I can hear it. Other is that you really need someone with competence, not a scam tech, to eval the system. You might get lucky and the stop leak works, but all other parameters of the system should be checked. For all you know, the evap just needs a good cleaning. They really suck to clean on some, but so very worth it!
Something you can do by yourself is get some Big Blue or comparable bubble solution and see if you can get lucky. First place I would go is those service valves. Here is another trick I have used. I put a balloon around each service port and see if they try to inflate after days. With a small leak, you likely would not see a leak in an instant, it takes time. Another leak area is the TXV valve near the evap coil. It would be under the sheet metal. I've got lucky on a couple where a flare nut was leaking and a little tightening fixed it. But you have to be careful there. Tighten nothing unless you can confirm a leak though.
But really, the smartest thing you could do is ignore the "favor friend" resources, and ignore the service contract idiots they want to send, and find a well vetted, 40-50yo independent tech, and be onsite with him to go over it. Unlike bigger companies that suck people into their web of BS with "free tune ups", independents rely on word of mouth and skill to get business. The rookies work in the big companies. The good ones venture out on their own. They could not survive with no ability. The even smarter ones get out of residential work all together! lol