I got the CB 1771 to finally stop leaking but it took a while.
My cover screws thread into bosses cast into the main body, but the threaded holes do not go all the way through the body so they don’t leak out the back. The original CB design uses threaded rod and wingnuts for the cover. Those got tossed for flanged, hex-head 10-32 screws with soft-ish nylon sealing washers to seal the screws against the cover.
The cover came with a formed seal that feels like neoprene and that got wrecked the first time I pulled the cover. In its place I just shoot a bead of that black, fuel resistant silicon caulk around the cover sealing slot and that has been sealing for several years, now.
IIRC, CB uses some sort of flat rubber washer between the breather and the filler pedestal and I couldn’t find a direct replacement locally so I went with a suitable, slightly stiff O-Ring squashed between the pedestal and the breather. I also bought one of those cool round, toothed, gland nut adapters for my ratchet drive so I can crank the breather up nice and tight with no leaks.
I only drain into the filler port so the drain port on the bottom has teflon tape on a pipe plug. The breather outlet ports on top have press-fit 90° plastic fittings (they are modified PCV fittings) going into 5/8” ID heater hose to each carb filter cover. I needed the bigger 5/8” hose to keep the case pressure down and it works. I do not vent my valve covers.
After all that........ The breather doesn’t leak and the only time that I get weeping from behind the crankshaft pulley is when I’ve been hammering the interstates at 80+ mph for over an hour or so and then I get just a little wetness at the drain lip in the tin under the pulley.
If I had it to do over again, though, I would probably just go with a Berg breather and declare success.