I'd avoid getting your head de-corked - that would just remove the remains of the cork rocker gasket

. A de-coke is what you're after.
If you can check the timing then a good thrash will de-coke it, but to be fair I think it's more likely that the knock sensor is the problem. One from a 2E Passat will do you. There's a couple up in Yate Breakers, if you're not too far away from them.
If you want an example of dealer-expensive, how about £40 for a breather pipe - it's just a single, simple pipe that goes from the block breather, to the rocker.
Now that smarted this morning!