For some of these dual evaporator models, in order to prevent defrost problems, the defrost thermostat or pipe thermistor had to be moved on a different part of the pipe in the fresh food section for some models.
In this case, it looks like different people not knowing their craft took turns working on it.
Since the appliance worked after them adding some stuff, but only lasting weeks, it's probably a leak on the sealed system.
A real tiny leak would likely have lasted 2-3 months, so if it's only weeks, the leak might be quite big.
Although I'm no refrigeration technician, I think any Whirlpool trained tech would likely have replaced the filter dryer with an UV ink one, vacuumed the system and recharged it to specified refrigerant weight on the 1st service call.
Then, wth the proper light and colored glasses, it would have been easy to find the leak(s) not just silicon caulk over anything they're unsure of. Might as well have soaked everything in a J.B. Weld mix
This seems to be a system with 3-way valve, making diagnosis a little bit harder. You can try adding an access valve to the succion side of the compressor and adding pressurized nitrogen so it would fill both evaporators to help find leaks on the low side and confirm if the evaporator coil has to be replaced. For any leak on the condenser side, if any, they shall be easy to find with the compressor running and proper refrigerant charge.
Reagarding solder type, most use Sil-Fos bronze alloy for copper pipes on refrigerators. Silver is used only to join the steel condenser coil. Silver brazing material can get too thin and be sucked in the small pipes, so yes it could clog a capillary.
I have seen in a few occasions small aluminium patches installed on the aluminium tubing of an evaporator coil, likely in case of a pinhole leak easy to see on the coil, never worked with them myself.