You say you lost all your refrigerant because the cap was leaking?
If that's all that was keeping it in, you're going to lose it all again.

When the system is empty you should replace the schrader valves.
That's easy and cheap.

The R12 filling capacity for W123 and W126 is 2.8 lbs.
Don't forget the oil!
200cc to a new empty compressor
40 cc for a sudden emptying of the system
20 cc for a new condenser
40 cc for a new evaporator
10 cc for a new receiver/dryer

Jeff