I would suspect to keep the throttle body warm in the winter and maybe prevent icing causing the throttle body to stick, my z16xe has the same and the pipe just runs straight through and out the other side, i dont know if its replacable, thats a job for greasemonkey but i suspect the car will be fine to drive providing its not leaking,

 

Story so far,

I went to work, left OH with instructions to phone vauxhalls to find out of there is a replacement pipe. At this point I am thinking the pipe that has broken is a corroded steel pipe.

Got email at work saying 1st dealer quoted £3.40 in stock, the the 2nd dealer -close to work- quoted £10.44 instock

sent email back for OH to find out what the discrepancy in price was for and to get a part number, only the part number was received by email.

After work, went to 2nd dealer with part number got part £3.40.
Parts dept guy says "Have you got the tap to tap it out with?"
to which I replied "isn't it the same thread?",
he shakes his head, so I'm thinking -Jeez! I haven't got time to tap it out, I had my hopes up for a straight swap-
Then he says something about the 'plastic pipe' breaking,
to which I say "plastic?, mines metal"
"metal?!!" he says "how did that snap"
"It was corroded and broke. Have you heard of these things snapping before"
"to the plastic ones, yes, but not metal ones"
"Ok maybe I'm mistaken, maybe it is plastic, I just assumed it was metal."

So I buy the bit and go home, on the way home I'm thinking -I wonder how the plastic bit is secured, is it threaded or a push fit, will it come out easily? How much is a full waterpump housing cover?

I decided best thing to do would be to go straight to the dealer by my house (dealer no.1) to ask those questions. It's easier to take something off when you know how it is fitted. There was a mechanic in the car park, so I asked him, he says he did one a few months ago, asked him how to get it out he says he used a screwdriver and it came out and then he just cleaned the rest that was left behind out of the threads. Asked him if he then had to tap a new thread, he said 'no the new one just screwed straight in' So I'm relieved a little and I go inside to find out how much the water pump housing costs. I'm at the desk with the bit in my hand, and he says straight away "they gave you the wrong one, there's two, a big one and a small one" I ask to see the small one. He brings it and it looks much more likely to fit, I say I'll buy it. He says £10.44. The observant among you will notice it was this dealer who initially said £3.40 and gave me the part number for the £3.40 part with the wrong thread, which led me to walk into dealer 2 (who initialy said £10.44) and gave me the part I had asked for which was the wrong part, but he didn't tell me there were 2 and there was now a better version costing £10!!!

Old part £3.40 wrong thread you have to tap a new one part number 90466779
New part (recently introduced by vauxhall) £10.44 allegedly correct thread straight swap £10.44 part number 55564351

Both identical except for the threads
Why on Earth did vauxhall not get it right in the first place and come to stupid solution of having to tap out a new thread?
Why on Earth is the new one so much more expensive when they are otherwise identical?
Why cut corners and design plastic parts in the first place FFS!!!

Going to have a go now at taking the plastic out, hope it goes well.

http://cgi.ebay.co.uk/Corsa-Water-P...-GENUINE-/330553692321?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4cf68910a1

 

The plastic pipe is a common failure and normally leads to head gasket failure as people dont realise whats happened,as you say you can buy a replacement part from vauxhall but its easier and quicker to replace the water pump in my opinion,costs a bit more but at least you have a new pump,i supply and fit many of these engines and i always replace pump if it has plastic pipe so as this cannot happen,as you say crap design