Lemme give my opinion....It's a 12 year old system, for a heat pump, it's past it's useful life or "wore out". Replace both indoor and outdoor unit. If money IS a problem, you can replace the compressor for a quick fix, just make sure the installer removes the indoor & outdoor piston and flushes the system out and makes sure that the "little hole" inside the piston is clear, (assuming it's a piston and not TXV) as well as check both coils for cleanliness, then install a suction line drier in the suction line just before it goes into the compressor. Just my 2 cents.