Air tools - rotary union

I bought a 50' retractable air hose from harbor freight. I love the thing but from the day I bought it, it leaked. After opening it up, it looks like a poorly designed part. Looking at picture 3, it's not exactly a precision part. I'm guessing some thick grease could help a little but I don't think it's going to fix my problem.

The in and out are just regular old 3/8 NPT. The only one I found so far is $85. It looks like it's a bit overkill for what I need. Is there something else I can use that is a little cheaper but better than the garbage that I have?

$130 Mosmatic 40.019 Rotary Unions WDG Swivel G1 3/8" NPTF G2 G1/4" M

https://www.amazon.com/Mosmatic-40-...56277&sprefix=3/8+rotary+union,aps,124&sr=8-6

 

I polished the inside with a Dremel and rouge. Added grease and now it's fine.

 

Did you get the Merlin on sale a few weeks ago for $69.99?
I bought one then. It does lose pressure, but slowly. Too slow to hear it leaking, and it takes about 2 days to depressurize my 4.5gal Dewalt.

 

It's a central machinery. After polishing and greasing it, soapy water shows no leaks. I don't know if the polishing did anything. At the very least, you should try grease.