Hi there, I'm fairly sure that since your car isn't metallic, that it won't have lost its lacquer (it shouldn't have any), but what you may have noticed is either fading due to red's reaction to UV light, in which case a light cutting or colour restorative compound will restore its lustre...Or, what you may be seeing is a previous repair's paint reacting with the UV (which would explain why only that part is affected). Both should be treated the same way.
But, if it cannot be restored, you may have to paint it yourself which must be carried out in a clean, dry & warm environment.
If the panel can be easily removed, then do so, as this will mean you do not have to mask off areas which do not need painting.
- Key the panel which you intend to paint with some lightly wetted wet & dry paper (circa 400 grit).
- Dry thoroughly, then a couple of light coats of primer (allowing 30 mins at least between coats) - this needs to completely coat the part to prevent reactions with the top coat. Use some (600 grit paper between coats to remove imperfections).
- 2 - 3 coats of colour (again, as with the primer use some 600 grit between coats, and allow for an hour at least, longer would be better unless you are applying heat between painting & sanding). Each coat should be progressively 'heavier' - but without 'runs'. Either bring the aerosol/paint gun closer each coat or make a slower 'pass' each time (DO NOT DO BOTH!).
- Allow to cure overnight (longer if possible), then use a light cutting compound with very very light pressure and a wax to bring to a shine.
As you can see, preparation and patience are the main factors to a successful repair. Ideally, you should allow a full 24hrs for a domestic job, less if you can keep the panel warm.
Haven't used the scratch repair product you describe, but when I repair scratches, I use an open-ended paper clip dipped in the brush of the touch-up paint and lightly dabbed into the scratch (this is after a light compounding first to reduce the scratch and freshen-up the paint in the immediate area) and fill the scratches with paint. Again, patience and a steady hand will work wonders.
Don't expect miracles, I always explain to clients that 'they' will still notice where the scratches were - because they know where to look, but to the casual observer, it should be near enough undetectable.
Hope some of what I've typed helps, and all the best with your repair - if I can be of further help, please don't hesitate to ask away.