You've clearly never owned an ex traffic car
I don't see why anyone would want to own an "ex police car"
they are "Rode Hard and Put Up Wet", thrashed to within an inch of their life ,hacked up wiring ,metal fatigue from doing "sleeping policemen" at 60 MPH etc .
abused more than a hire car that Jamie (TB) dislikes
My HBV was the original factory item ,2003 ,so 20 years old ,had only just started dripping last week, replaced PDQ ,once the engine was cooled and the SKUTTLE and WIPER MOTOR was REMOVED
I'm not saying that doing the job by removing the plenum is a bad idea , but that route isn't issue free either, if done badly ,plenum seals .O-rings etc are not easy to get these days ,it's pretty important all the breathers are put back correctly etc ,not a job I'd want a "quick fit fitter" or unfamiliar grease monkey doing
the original poster doesn't want to do the job ,so farming it out to a local garage ,which have probably never seen an Omega on their ramps .
the HBV is a pretty simple DIY home mechanic job ,which, if done slowly and with care ,should go without problems or other parts needed
Other than 3 new ,good quality jubilee clips to replace the ****ing GM spring hose clamps