Update: I ran it with a diagnostics tool connected and once it had warmed up it kept flipping between "Slipping lock up" and "Fix lock up" every now and again on a fairly flat surface at a constant speed. Yes, when it was in 'geartronic' it seemed ok. The gearbox doesn't seem to be noticeably slipping otherwise.
I also looked through the receipts I got with the car. They were all mostly main dealer up until two years ago (it was very well looked after) and there was no mention of the transmission fluid being changed or topped up (this was listed on the dealer check list as 'n/a'). I can therefore assume that it has never been changed.
I have been quoted £200 by my local reputable garage to change the transmission oil, of which half the cost is the oil and the rest being labour. I have seen second hand gearboxes on eBay for £500 (condition questionable?), and £1,800 +vat for a new gearbox.
This car has been otherwise reliable and apart from £400 for new front shocks hasn't cost me much in maintenance (it did also cost £300 for three new tyres and £250 for a spare key). I only bought it in March this year for £1,800 but what with all this and my last car being destroyed by an engine fire at the start of the year* I am wondering if I am cursed and I should just put it on eBay for £800 and go and get myself a pedal bike...
*
https://www.kentonline.co.uk/maidsto...r-park-199942/