That would be a Layrub coupling you have there then! or not as its probably giving up and you have serious transmission vibration?
They were only fitted to one other road going vehicle that I know to (for our size), the humble Bradford van!
This is what I think you are looking for?
I did have a load of tech info on these items but cant find it at the moment I did get a replacement a good few years ago from my local prop guys over at Proptech Ltd.
Unit 81, Hartlebury Trading Estate, Hartlebury, Kidderminster, Worcestershire, DY10 4JB.
Tel: 01299 251247
Martin's the guy to ask, I think it was about £120 at the time.
Also I have found these people, don't know anything about them but might be worth a call.