Leaking Refrigerant, My problem or dealers?

The leak appears to be in the line between the outside unit and the inside unit. When the dealer installed the new A/C unit they did not replace the line from the outside unit to the inside unit, they reused the old one.

Should they have replaced the line? Is it standard to reuse the old one?

Can the old R-22 line handle the higher pressure 410A refrigerant?

My old system never leaked.

Don't know, somebody will. What I do know is that some of the refrigerants can be used with coils that are contaminated with older stuff and some can't. Normally, the coil is a little different and your efficiency may not be up to where you expect it if the compressor, refrigerant, and coil are matched up.

Depends on what the contract read and where the leak is. If the leak is where the new unit was braised to the old line then they pay. If the leak is just somewhere in the middle and the contract said they would use the old line you pay.

So there is generally no harm in reusing the old line?

line

The line is "neutral" in that it does not really care what is inside it, the difference is the units at either end.