Im not saying this is your issue but I have had 2 "Yong Heng's", the first turned out to be a fake, it had 2 rings on the secondary, high pressure piston and I also got black oile during the first tank fill.
That compressor lasted about 50 hours...
My second one has been running for 170 hours over the past 2 years and still has good pressure and I also took the secondary high pressure head off of it when I got it and yes, it has three rings on the piston and I never had black oil. I change oil every 50 hours and my last change was a dark brown, not black at all and no 'glitter' in the bottom.
Also, you are NOT using high pressure compressor oil, I can jus6t about guarantee you that if it's not "breathing compressor oil", it's not the right stuff.