Symptoms are:
Loosing coolant (about 1litre every 1000 miles, but is increasing)
Feels down on power
Hesitant upto 4000rpm
Complete bugger to start when cold, and then is firing on 5 cylinders, possibly 4, for about 10 seconds and then runs fine.
Since owning the car:
New oil cooler fitted 12 months ago
The HBV was replaced 12 months ago with a new GM item.
I replaced the headertank about 8 months ago, aswell as a new pressure cap too. (both from VX)
Plugs, Leads and Coilpack replaced about February (GM item) - this did not solve missfire.
Since having the car, I've done a complete coolant flush, and the system is now the proper mix (coolant is a nice pink colour) the coolant does not change colour either, and remains pink.
Oil has been changed regularly, but it soon turns black (say after 2.5k miles)
Also, there is an oil leak from between the block and head on the passenger side (originally assumed it was the cam cover gaskets, so I've done them 4 times now, and replaced the cam cover with 2 others (1 second hand, 1 brand new)
Personally, I reckon its heads-off time... although banging in a 3.2 is more appealing (IF I can find one...)