Mine has gone, and gone again... all since I put a standard exhaust on, which is probably unrelated but I thought I'd give you all the information.

Instead of just changing the gasket and short of changing the head what is the best course of action? Linish the exhaust manifold?

A pair of them expensive gaskets with a smear of exhaust paste sorted mine out.
I absolutely hate exhaust paste usually but I thought it was worth a go and it worked for me.

The exhaust gaskets will burn again and again if the head is prevented from turning when exhaust stud nuts are fasten. The head should only be fasten with 1 kg or less for the head to turn. This way the gaskets have good contact on both manifold and head.

i always fit the manifold without gaskets before doing the head nut routine then remove the manifold, grease the gaskets with copper grease and torque down

never had an exhaust gasket blow yet.

new gaskets fitted - tighten the manifold - back off the head nuts then re torque then finally torque the manifold it lets the heads align with the manifold as Viking says.

the other thing to check is when a stud or a bolt is fitted in a flat mating flange the material tends to pull up around the stud or bolt hole when new the threaded hole would have been countersunk to allow the flat area to mate with the gasket. On any heads im working i remove the studs, if i can, countersink the flange and run a flat file over it to dress it back down - leave it a bit rough so as it bites the gasket. Its unlikley the steel manifold is the problem most probably its fitting technique and worn head
(dont panic JW yours will be fine )

I've used bronze high temperature silicon sealant in addition to the gaskets and this tends to do the job too.....

Thanks for the advice, I'll re-torque it all and get some new gaskets on it as soon as I get my hands on the torque wrench.

You have flat-plated the fanny mould havent you...?