If you got that many apples from a 3rd year seedling you are incredibly ahead of the curve. Seedlings can take a long time to produce. I know nothing about what diseases or pests are common in France but my understanding is that you are in one of the best fruit growing regions in the world. Research the local diseases and spray if you have to. Don't overspray but sometimes it can be extremely difficult to grow perfect fruit without the use of fungicides and insect killers.

Since Bramleys are cookers, they don't need to be perfect to be usable. Unless you are baking the apple whole any manky bits can easily be cut out when you chop the fruit for your crumble, sauce or pie. The tree I know best seldom has any problems and essentially looks after itself. There may be the odd Codling Moth hole some years but they crop so heavily it isn't an issue.

BTW, Speedster, 'Bramley Seedling' is the full name of the cultivar. It doesn't mean it's a seedling tree.

Thank you for your rapid and helful responses. I'll deal with the list fo possible pests next and report progress.