Hi Wke.
Dazz is right - my dealership caused my problem but wouldn't admit it (no gas meant the magnetic clutch wouldn't operate the compressor). However, they replaced the condensor unit (eventually) and that seems to have cured whatever leak they'd caused.
It's not unheard of, though, to need a regass from time to time. I think it all depends on how much use is made of the aircon; some say you need to run it for 10 minutes a week to keep the seals in good condition, others say to just use it when you need it. Is it hot in Belgium right now?