If you have the newer Matco (Parker) split style rotating parking brake valve, it is prone to leaks at the split joint if the mounting screws are not torqued properly and evenly, or mounted without the rubber washers. Not saying thats where your leak is, but it is a possibility. I had so many problems with mine on my RV-10 that I removed it and replaced it with the older single block style. No matter what I did, it would shortly start dribbling at the split where the shaft passes through the blocks. On my RV-9A, I was able to find a NOS single block valve and am using that.
RV-10: #41686 Under Construction
RV-9A: #90949 Under Construction
RV-10: #40637 Completed/Sold 2016
Cozy MKIV:#656 Completed/Sold 2007
"Donor Exempt" but donated through Dec. 2021