There is an ac pipe which runs from condenser under battery tray,along chassis rail to the bulkhead. They are poorly fitted and rub thru on the rail .good news is they are available new from gm approx £60
Not an easy replacement, abs pump is in the way, and couple of electricky connector's, under the battery tray, also pipe has two clips on chassis rail, 
I had a leak from this very same pipe where a pin prick of a hole had developed from movement of the pipe on a previous Omega. Spoke to a tech friend at VX about its replacement and he pulled his face saying it's an awkward job, and he also stated it required the ABS pump moving to get at it. From memory, I think he said VX quote about 5.5 hours for the job, which is an indication that it isn't that simple a job!
Just removed said pipe from my breaker, which has no engine,or gearbox in.
Abs,pump has to be removed, two elecriky plugs hidden under battery tray, it then comes out towards the bulkhead..
With the engine and radiators in be a Bastid job.