We have a small leak that from the oil pan I want to fix on a 2009 1.4l petrol engine - BXW.

ERWIN describes that the exhaust which runs a handwidth under the pan has to come off.

Has anyone removed the pan without removing the exhaust header pipe?

Also it states that a special VW cleaning and degreasing agent should be used. How special does a cleaning and degreasing agent have to be?

First thing you should probably do is work out why it's leaking, because with modern engines that can be a symptom of the real fault, rather than the fault itself. I'll do some research on the BXW set-up and get back to you a little later.

If it's anything like BKY, doing it with exhaust in place would be horrible.

Looking at this page (and ebay pics of the sump) it's not as bad, and may be doable without too much grief with exhaust in. https://skoda.7zap.com/en/cz/fabia/fab/2009-608/1/103-103007/#21

A few of the sump screws towards the gearbox end of the engine will be harder to get straight-line access to, but with care that shouldn't matter too much.

 

The thing to check first, if it's never been visited before, is the oil separator module on the back of the block, item 19.  If that's blocked up it will tend to increase the pressure within the crankcase, promoting seal failure.

 

I certainly wouldn't worry about special cleaners, probably just speeds things up for techs in dealerships. 

Also check that the source of the leaking oil is not from one of the 2 O-ring seals for that oil separator - these did, for a period in production, end up being known to cause a oil leak, I bought a pair to sort a slight leak on a BXW engine in a late 2009 Ibiza, but it was sold on before I sorted that!

I will probably have a go at the weekend. The leak is from the oil sump seal.