MCNS,
80190 is a power brake booster check valve that is claimed to fit most Ford, GM, and Chrylser. This number is a Dorman/Motormite number found extensively in the US. I'm sure there is a common equivalent in Canada.
The advantage over the XS650 Yamaha breather is they are quite small and can fit into a crowded battery box. The disadvantage is they do get gunked up and must be replaced, where the Yamaha valve is probably more efficient and can be cleaned.
I'd love to try the Yamaha (and will on my next project) but with fuse boxes, relays, mastercylinder, 3-phase regulator/rectifier, etc., I can't seem to find a place to mount one on my 850 test mule.
By the way, Mike's XS site doesn't seem to list this any more.