Autobarn charged me like $45 for it.. I just said "I want a bosh plastic blow off valve" and got the right part. Then got a bit of radiator hose with a similar diameter, cut it up and it all fitted nicely.
Generally you can tell with a 7MGTE BOV if it's leaking... if you lift off the throttle sharply and you hear a shudder "ch ch ch ch" rather than a single "fooch" then your valve is probably leaking and you can hear the compressor surging. I recommend replacing it if it is making this sound - can foul your plugs, lose you hp, wreck your turbo (debatable), make the car stall... lots of things. Fix it while it's only slightly broken