I have 3 out of the 4 tyres leaking down to @ 1 bar after only a week. Garage suggested it may be dirty / corroded wheel rims. Is this a common Copen problem?
Are the wheels in good shape, no punctures or excessive wear? First thing I would do (after making sure the tyres are ok from the outside) is separate the tyre from the rim, look for irregularities, clean everything up and put them together again. I had a leaking tyre once because of a tyre valve that was stuck open. Apart from that no problems at all (excluding mental ex-girlfriends with a sharp knife )
The man at my local Kwikfit persuaded me that it was indeed a dirty rim problem and he sorted it out in half an hour at very modest cost.