Brunner air compressor help

[WastedAgain440]

I have an old brunner compressor, think it's overdue for an oil change but I don't know what oil to use. My dad was the last one to change the oil in it and he has passed away.
Can't find any info online on what oil to use or capacity. It's a Brunner comp. model A5301

 

[Fixnair]

I've worked on compressors for 50 years and the best oil you can use for the money is 20 wt hydraulic oil. If you can't find hydraulic oil look for non detergent automotive oil. Not as good but will lubricate the bearings alright. 30 wt is generally too heavy unless your ambients run over 100*.
Do not use a synthetic. The crankshaft seal will be dissolved and any other elastomer that they used back then will not tolerate the synthetics.
I would also think 4 qts. Would be enough to change the oil.