Another Shoebox Compressor Question

The small vent hole on the side of my shoebox is venting a small amount of air during operation. I believe the problem is the very small O-ring that sits inside the space where the vent knob is located. Anyone know what size 0-ring I need for replacement. It is NOT the burst disk.
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The small vent hole on the side of my shoebox is venting a small amount of air during operation. I believe the problem is the very small O-ring that sits inside the space where the vent knob is located. Anyone know what size 0-ring I need for replacement. It is NOT the burst disk.View attachment 331757
I’m following your thread as I have a similar issue.