Heat Pumps and Electric Heating - Bad ETV on Trane Heat Pump

My 10 yr old Trane XE1200 has been icing up and I just had it checked. The tech appeared to be very thorough, checking pressure and temperatures. He determined that the expansion valve is faulty due to improper temperature readings. He also stated that the drain pan is beginning to rust. He advised that it would run approximately $700 to replace the valve and drain pan. His recommendation is to have the evaporator coil replaced so it would have the 5 yr warranty and would correct the problem which he stated would run around $1600. He stated average life for the coil is 10-15 years. His company is no longer doing repairs in my area but recommended another Trane dealer so I don't think he was trying to guide me to the higher priced repair. What would you recommend, to replace the valve or replace the coil on this 10 yr old system?

id change the valve and just clean the coils if your not haveing any problem with them unless you leave by the sea then they might go from salt