Top with R12 if you can get it, I just got 2 cans put in from a friend.
But my friend says he has for 7 years topped off R12 systems with R134a
with no problems yet, even his own car, but they say the oils dont mix.
R12 cools better , get R12 if you can even at 60$lb, no I cant get more
R12, I need one more can myself.