Evaporator Coil Replacement Under (Parts) Warranty

My Goodman evaporator coil is being replaced under warranty (4 years old) which they 'sniffed' a refrigerant leak in two places. They stated because it was in the garage that I have been doing woodworking in that likely there was corrosion over time from particulate matter getting past the filter (does this seem like a reasonable explanation). Does $1650 seem reasonable to replace the evaporator coil (part under warranty labor not) and recharge...they said 13lbs of refrigerant which the unit takes like 9.5 and a 30ft run so it seems like 10 is more like it, not 13. Location Arkansas. Thanks!