On one occasion in 2004/5? after some disruption there was a 180 doing the inner GWML relief line stopper to Paddington instead of the usual 3 car turbo during the morning rush hour. Quite an upgrade!
Well

. I'll say 2 occasions when I expected a Turbo and a 180 turned up...
Mum and I were coming back from Plymouth to Didcot Parkway on January 1st 2006. I think it was mid-journey I or we discovered there were no buses on route 35 from Didcot back to Abingdon. So when we got off the 12:25 Plymouth to Preston service at Bristol Temple Meads we managed to get an extension to Oxford. Thank goodness we had about 40 minutes at Bristol Temple Meads before the 15:10 (HST) to Didcot.
When we got off the HST, we had about 20 minutes before the 16:31 to Oxford (Worcester Shrub Hill). Imagine my delight when a 5-car 180 rolled in considering Turbos regularly run. So technically it was the best rolling stock substitution even if it was booked for a 180 at the time.
The second occasion was when I came back from Paddington to Didcot Parkway on the 17:18 I think in January 2017. According to the timetable change (December 2016 one it would have been) board at Didcot or in my Guide to Services, this was meant to be a Turbo - a 180 it was instead. Pleased of course. I believe the 180 substituted - even had a trolley service onboard even though it didn't say in the timetable.