2013 VW Golf GTI A/C - Slow Leak

[jfklein]

I’ve had a slow leak in the A/C system on my 2013 VW Golf GTI for over a decade. I bought the car in 2015 so it's likely leaked since it came from the factory. A couple years ago, after at least three previous attempts, a repair shop finally located the leak using soap bubbles, at least that’s what they told me. Apparently it was coming from one of the service ports. They said the Schrader valve is ok (they had replaced both), but the seat that the Schrader valve seals against at the bottom of the service port is defective so the leak is coming around the valve, not through the valve.

The pipe segment that the service port is attached to would have to be replaced to fix the defective seat, which would be very expensive. So to seal the leak they said they applied silicone to the service port cap threads. I thought this had fixed the leak. But two years later the A/C is barely working again, following the same pattern of the previous times the refrigerant leaked out.

Assuming the shop’s diagnosis was correct and the leak is coming around the Schrader valve, here are my questions:

From what I understand the service port cap is supposed to provide the primary seal at the service port and the Schrader valve is just used for sealing when filling and testing the system. So this means the service port cap is also defective and not sealing the service port correctly. Is this correct?

The factory service port caps are plastic (see attached photos). Should I get some generic aluminum service port caps that can be torqued down tighter than plastic caps in order to seal the service port?
Example:
https://www.z1motorsports.com/all-sale- ... 9512.html

Google Gemini said a product called Nylog Blue should be used to seal the service port cap when it is screwed on. Is this recommended?