Gluing vinyl

That's interesting. I used CA (super-glue) when I did my RoboCop, Batman and ED-209 models and never had a problem with them coming apart. I think part of it is having a good secure contact between parts. But others may have different thoughts.

Knight has a good point about the secure contact between parts. Regular CA does best when there is very little gap between the parts. An easy way to check exactly how much area is in contact is to color one of the surfaces to be bonded with a dry erase marker, and then mate the surfaces. The ink will stick to the high points of the uncolored surfaces, and these should be sanded down.

Do you know exactly what kind of plastic it is? Vinyls refer to a family of plastics. In my experience, some of them don't bond well at all, regardless of glue (this is especially true of polyethylene and polypropylene, though I doubt your model is either of these). In these cases, I've had better luck roughening the surfaces (if you can create holes larger at the bottom than the top, I'd do that too). By doing this, you're creating recesses which the glue can seep into, thus the bond is secured by the mechanical forces within the glue rather than the molecular forces between the adhesive and the plastic. Epoxies and gel superglues work better for this type of interface.

Sounds like you put a side load on the part. CA doesn't hold well when a shear (sideways) load is put on it.

Thanks for the suggestions,
Luckily this is a genuine Horizon kit and not some dodgy remould, so I have both the box and the instructions.
Unfortunately the instructons are written with the younger modeller in mind and don't say what the composition of the model is beyond describing it as 'poly vinyl', but they do say to use a cyanoacrylate for the adhesive (listed in the tools as 'Krazy Glue').
Thinking about it, I may have violated one of my strict preparation rules by not washing the parts prior to assembly, do you think mould-release residue may have interfered with the bond? I intended to wash the completed model before priming for that reason.
There is one piece of good news, after I had originally glued the model together I discovered it wasn't very stable and wished I had filled the legs with clay or plaster to balance it better, I will do this now as it would have bugged me if I had left it.
As regards the amount of load I put on it, I assure you it was very slight, if I had broken the model I wouldn't have posted about it, I would have just re-glued it, it was the ease of the break that alarmed me. I realise I will have to be extra careful with this, my only vinyl model.

Neil.