Xone DB4 - temperamental FX buttons

Hi

I just got a DB4 for an absolute bargain (£800!!). As expected at that price there is a slight issue in that the FX on buttons below the faders are a bit hit and miss, they’ve obviously been hammered the most by the previous owner.

Does anyone have any advice on how I might be able fix or improve them? Or should I just look to send it to A&H for repair? The previous owner claimed it has been recently serviced but I’m not so sure, at least not by A&H.

Thanks in advance…