Thetford fold-down sink won't stay up

[Powertrain]

In the shower-toilet of our 2003 Autosleeper Executive we have a Thetford unit that includes a plastic sink that folds down and when not needed folds up and clicks shut - at least that is what used to happen.
Now it stays down and will not stay up. I found two small pieces of plastic moulding in the base of the hinge secrion so I have assumed that something has given up.
I can't believe this is a rare problem so request you experts to tell me:is there a recommended fix or modification for this problem?

 

[kenjones]

My Topaz had a similar problem, the sink would drop down if i drove over a pothole or speed bump.
The first and very effective fix was to fit a plastic turnbuckle ( bought from a caravan dealer) on the sink surround so it held the sink closed. I noticed a few vans in dealers had the same mod.
Not sure if your van uses the same unit but it will be similar.
Since then I have had a problem with inside of the unit behind the sink falling apart. The sink which catches the waste water when the hand basin is tipped came unstuck as did the inside of the cuboard behind the toilet.
I have re fiixed the inside of the unit and the folding sink now works properly. ( I still use the turnbuckle but it's not really needed.)
With hindsight I think the initial fault was caused be the innards of the unit coming loose.
Hope this helps.