Tweeter, I JUST finished converting my Vevor compressor with the Yong Heng head over the weekend. I haven't had the time yet to fill up a tank, but on quick initial test, everything works. You're correct, the bottom end (crankcase and mounting points) are the exact same on the Vevor and Yong Heng. It cost me $150 for all the conversion pieces.I've been meaning to write up a post on my experiences, but life keeps getting in the way. When I got my Vevor, I had oil coming out of every fitting, hose, etc, and I did a full tear down before running it. What I found wasn't pretty...the metal castings are really rough with tons of slag left on it. The mfg then paints over the slag with silver paint, assembles the compressor and runs the compressor to "break it in". My compressor had metal shavings/slag everywhere...all the way up to the second stage. Just doing oil changes won't get all the crud out, you have to go through piece by piece to clean things out. There is a rubber screen/gasket thats right behind the crankcase cover, and it will prevent metal shavings from draining out with the oil when you do a oil change. The metal shavings like to get stuck to the rubber screen and stay inside the machine instead of getting drained out.My recommendation to you is to tear it all down, and clean it out. In my case, I had metal debris sitting in the crank, piston ringlands, and second stage compression orings. If I had to take a guess, I'd say that you probably have a damaged oring in the second stage. If that's the case, it's a easy fix and I think they included some spare orings with the Vevor originally. Finding parts for these compressors is an adventure. The search engine on AliExpress is garbage (and parts aren't sold on ebay). The most effective method I've found is to have a picture of whatever part you need, and then message sellers on AliExpress asking them if they can sell the part. You might get lucky and they'll already have a product link to send you, or (like in my case) you'll have to wait for them to create a new item listing so you can purchase it. If you can identify the parts you need, I might be able to help you source them as well.
Leaking from the pipe and flange nut? Check if there are scratches on the conical nipple.If there are you could chuck it on a drill chuck if you have large enough, and use a fine file to smoothen the cone while rotating it in the drill. Kind of like a miniature lathe. Marko