Oh no rounded overdrive plug!!

[RobH]

They are widely-sold here too Don . e.g: 

https://www.amazon.co.uk/dp/B0GC5CMQD5?tag=bestnewdeal09-21&linkCode=osi&th=1&ascsubtag=ecSEP1mk2jmoiqev7z

[keith1948]

Had same problem a few years back. Took od plus gearbox to a rebuilder and apologised for rounded off nut. No problem was the reply. I watched as he gave it a smack with a hammer and it then turned off as easy as pie. He had worked on the od production lines so knew how to do this. Practice made perfect. A novice would probably break the od casing. 

Keith