You have a Danfoss BD 2 or BD2.5 Freon R12 unit unless there there is a Blue sticker on the other side stating 134a refrigerant. Around 1995 there were a Few BD 3 compressor
conversion to 134a that also changed oil
from mineral to ester oil
comparable with 134a refrigerant.
do not use 134a refrigerant as there is plenty of R12 around and you only need around 3 ounces. Your problen then is this a one year loss of refrigerant or a one month loss.