I have a 2001 1.6 Octavia. About 6 weeks ago the engine management light came on intermittently at first and then all the time and the car started to run roughly.

I took it to a garage who diagnosed a misfire in cylinder 1.

They did a full compression check of cylinder 1 and it was fine, then they changed the HT leads and it made no difference,

In the end they put in a new spark plug and  it ran fine.

About three weeks later it did the same and I found it was cylinder 1 again by removing the HT lead and it making no difference to the way the car was running. 

Another new plug put in and it runs perfectly until this afternoon when Cylinder 1 spark plug is again not working.

Every time the plug packs up there is no exterior sign of damage to the plug - no burn marks or splits in the body - the only think you can see is it is 'wet' from where it is not burning the fuel.

Does anyone have any idea what would make the car damage spark plug 1 and no other plug like this?

 

Thanks

Headgasket?