I'm looking for some guidance in recharging the R-12 A/C system in my "new" 82 300D. The car only has 78k miles, but has been sitting in a garage since 1999. My manifold gauge set reads 9 psig when connected to the suction side(engine off). I assume the charge leaked out over the last 11 years. I momentarily jumped the low pressure switch wires to confirm that the compressor would engage. I have two 12oz can of R-12 available. Should I:
1. Add the R-12 that I have and hope for the best
2. Evacuate the system ... Then flush and replace compressor, expansion valve, dryer, etc., then recharge with R-12.
3. Something between 1 and 2

Thanks in advance