They told me that when removing the front diff air duct to access the oil, two bolts were heavily corroded and the heads had sheered off so they had to drill out the bolts. Here's the funny part- they then said I have to pay an extra £181 for the cost of them fixing their mistake!!

I literally burst out laughing and asked if this is an April Fool's joke. Service manager just looked at me and sheepishly said no...
After explaining to them that firstly a couple of bolts costs about £1, and secondly (more importantly) this was their f**k up which they didn't bother to tell me about until collection, they agreed to waive the charge. I agreed to wave them good-bye forever!!