Three possible leak points, the rear seal that connects to the booster, or the top two seals that connect to the fluid reservoir.

https://www.fcpeuro.com/products/vw-brake-master-cylinder-dansk-251611021c

My bet would be the top seals.  Look for cracks/leak points.  If you use a sealer like silicone, take extreme caution as not to introduce into the brake-fluid.
https://www.gowesty.com/product/hydraulic/24178/brake-fluid-reservoir-?v=

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Tom C
Sent: Wednesday, March 16, 2022 1:25 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Brake master cylinder weep

Hey Guys,

I think my brake master cylinder has a slight weep. It’s not visibly
leaking anywhere it just looks slightly wet we’re it bolts into the booster
and it seems like it’s very slowly and gradually making its way down the
booster onto the wires and then a little drip. What do you guys think?  Any
advice would be greatly appreciated. Thanks tom