Oil out air cleaner
 

Any tricks to rule out a pressure relief valve being stuck open?
(2000 Vulcan 1500 Nomad)

I don't think there is a pressure relief valve.
Has the problem just started or did you just buy the bike ?

Does the bike have an aftermarket air filter such as a K&N ?
Was the K&N filter over oiled ?

open your air cleaner, start your bike, in neutral, on level ground, look where your filter was, if you have more than 1 drip for every 30 seconds from your crankcase vent, you probably need a engine overhaul....
If its just oil isv dripping from the cleaner after a month or 2, thats normal....