[qaz996]

I'm not sure I follow the diagnostics.

Your refrigerant was recharged, then a few days later they drained the system, noted a difference in weight and proclaimed a leak from the evaporator?

Leaks in the A/C system can be found by a "sniffer", as Princeton mentioned or the more common UV light on fluorescent dye in the refrigerant. 95% of the A/C components are pretty easily observed from underhood or below the cowling, so it should be fairly easy to check those for leaks with a UV light and yellow lens glasses.

That leaves the evaporator and the 18" or so of piping into the climate box not visible from the engine compartment. Though it is difficult and uncomfortable, with a mirror and UV light, one can in fact see a leak from the evaporator through the cabin air filter box.

 

[qaz996]

I would say no, the XC60 (or any Volvo evaporator in past 20 years or so) are not known weak points. I have seen a few leaking evaporators in my 8 or so years but I would never say they are known weak points. More often on XC60's, I see leaks in/around the TXV.

The dealer (and all Volvo dealers USA) give lifetime warranty on parts/labor and their price is more than half off the other shop? Easy decision in my opinion.