It might well be, if the kit is so old, that the plastic has 'matured'. Some of the Monogram kits from that era used a fairly hard plastic, and this might have changed over the years, becoming glazed, to the point where it is not reacting to cement. I'm not familar with that particular type of Revell adhesive. Is it actually polystyrene CEMENT, or glue for plastics?
If it is a glue, then the same result will be found with it, and with any 'Superglue' - it will bond, but will very easily separate. This is because the mated surfaces are only bonded by the glue, and not a chemical reaction.
With a poly CEMENT, it is not only the adhesive that bonds; the mated surfaces of the plastic are melted slightly by the reaction, and are fused together. You will have probably found that the liquid poly has done a better job, but has not got the strength. This is because, being thinner than 'tube' cement, it has not 'penetrated' the surface of the plastic as much, which is the the aim of liquid, as it's used for finer work, where the least amount of damage to the smaller components being joined will occur.
What I would suggest, is to first wash the parts, if possible, then abrade the joint surfaces, either by sanding, or by scoring with a scalpel or similar. You will need to remove any dried glue/cement first. This should cut through the hardened outer surface of the plastic which, in effect, has become resistant, rather like an armoured coating, due to aging. You may have noticed that the surfaces, before having adhesive applied, were fairly shiny.
If the Revell product mentioned is a cement, then it should begin to work. If it is not a cement, then you will need to obtain one. Normally, Humbrol and Revell 'regular' cements work exceptionally well, as do most other well-known brands, but some, such as 'Bison', are more glue than cement, and are best avoided when a clean, strong joint is required.
Note that any areas where 'Superglue' has been used, will need thorough removal of that glue. Superglue will not adhere to itself, and neither will other adhesives stick to hardend Superglue.
Another reason this could possibly be occuring, is too much cement being applied. As the adhesive cures,the reaction with the plastic is weakened, as the cement is bonding more to itself than the plastic. This is normally evidenced by what at first seems a good, dried joint, but one that will seaparate very easily as soon as any pressure is applied against it.
Before attempting any of the above suggstions, it would be a good idea to experiment with them on some of the sprue from the kit, treating it as if it was the kit parts. This should give an indication of which action to take.
Hope this helps, good luck,
Terry.