Repair vs Replace AC

[Wesemiorn]

We have a 12 year old Trane AC system. No serious problems until now. Evaporator coil is leaking. What are pros-cons of replacing evaporator coil vs replacing whole system for $8,000 plus. We must consider that the existing refrigerant will only be available for another year and so no future repairs will be possible without replacing the system. Also, we will likely be here for about 10-12 more years.